How to resolve heroku "You are trying to install in deployment mode after changing your Gemfile" error?

Question

I know this question appears on SA already---but, nothing is resolving this issue for me. I understand that this simply indicates that my gemfile and gemfile.lock file are out of sync. Removing the gemfile.lock file and re-bundling should resolve this. I have tried a number of attempts at tweaking my gemfile, commit, and pushing---but, nothing has worked. Anyone familiar with this heroku stack-trace who can offer some guidance? This changed for me suddenly.

Attempts:

- remove gemfile.lock and bundle install
- update bundler
- remove older versions of multiple installed gems
- 

git push heroku
 Counting objects: 41, done.
 Delta compression using up to 4 threads.
 Compressing objects: 100% (40/40), done.
 Writing objects: 100% (41/41), 5.64 KiB | 0 bytes/s, done.
 Total 41 (delta 27), reused 0 (delta 0)

 remote: Compressing source files... done.
 remote: Building source:
 remote:
 remote: -----> Ruby app detected
 remote: -----> Compiling Ruby/Rails
 remote: -----> Using Ruby version: ruby-2.3.1
 remote: -----> Installing dependencies using bundler 1.13.6
 remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
 remote:        The git source `git://github.com/rails/sprockets-rails.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/sinatra/sinatra.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/jonatack/will_paginate.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/kesha-antonov/simple_form.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/sonalkr132/spring.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        You are trying to install in deployment mode after changing
 remote:        your Gemfile. Run `bundle install` elsewhere and add the
 remote:        updated Gemfile.lock to version control.
 remote:        You have added to the Gemfile:
 remote:        * source: git://github.com/jonatack/will_paginate.git (at master)
 remote:        * source: git://github.com/kesha-antonov/simple_form.git (at rails-5-0)
 remote:        * source: git://github.com/rails/sprockets-rails.git (at master)
 remote:        * source: git://github.com/sinatra/sinatra.git (at master)
 remote:        * source: git://github.com/sonalkr132/spring.git (at bundler-dep)
 remote:        You have deleted from the Gemfile:
 remote:        * source: https://github.com/jonatack/will_paginate.git (at master@3c86149)
 remote:        * source: https://github.com/kesha-antonov/simple_form.git (at
 remote:        rails-5-0@a1561c9)
 remote:        * source: https://github.com/rails/sprockets-rails.git (at master@6fa795a)
 remote:        * source: https://github.com/sinatra/sinatra.git (at master@63e81bc)
 remote:        * source: https://github.com/sonalkr132/spring.git (at bundler-dep@0caed19)
 remote:        Bundler Output: The git source `git://github.com/rails/sprockets-rails.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/sinatra/sinatra.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/jonatack/will_paginate.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/kesha-antonov/simple_form.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        The git source `git://github.com/sonalkr132/spring.git` uses the `git` protocol, which transmits data without encryption. Disable this warning with `bundle config git.allow_insecure true`, or switch to the `https` protocol to keep your data secure.
 remote:        You are trying to install in deployment mode after changing
 remote:        your Gemfile. Run `bundle install` elsewhere and add the
 remote:        updated Gemfile.lock to version control.
 remote:
 remote:        You have added to the Gemfile:
 remote:        * source: git://github.com/jonatack/will_paginate.git (at master)
 remote:        * source: git://github.com/kesha-antonov/simple_form.git (at rails-5-0)
 remote:        * source: git://github.com/rails/sprockets-rails.git (at master)
 remote:        * source: git://github.com/sinatra/sinatra.git (at master)
 remote:        * source: git://github.com/sonalkr132/spring.git (at bundler-dep)
 remote:
 remote:        You have deleted from the Gemfile:
 remote:        * source: https://github.com/jonatack/will_paginate.git (at master@3c86149)
 remote:        * source: https://github.com/kesha-antonov/simple_form.git (at
 remote:        rails-5-0@a1561c9)
 remote:        * source: https://github.com/rails/sprockets-rails.git (at master@6fa795a)
 remote:        * source: https://github.com/sinatra/sinatra.git (at master@63e81bc)
 remote:        * source: https://github.com/sonalkr132/spring.git (at bundler-dep@0caed19)
 remote:  !
 remote:  !     Failed to install gems via Bundler.
 remote:  !
 remote:  !     Push rejected, failed to compile Ruby app.
 remote:
 remote:  !     Push failed
 remote: Verifying deploy...
 remote:
 remote: !  Push rejected to xxxxxx.
 remote:
 To git@heroku.com:xxxxxx.git
 ! [remote rejected] master -> master (pre-receive hook declined)
 error: failed to push some refs to 'git@heroku.com:xxxxxx.git'

Answer 1

to force heroku to use the https:// instead of git:// protocol, add BUNDLE_GITHUB__HTTPS (note the double underscore) as an environment variable and set it to true (in your heroku app's dashboard under the Settings tab in the Config Vars section).

Answer 2

Most answers simply indicate to delete gemfile.lock and run bundle install. However---there is a new message popping up bundler regarding https:

The git source `X` uses the `git` protocol, which transmits data without
encryption. Disable this warning with `bundle config git.allow_insecure true`,
or switch to the `https` protocol to keep your data secure.

following the message prompt created a new config file in ~/.bundle/config. This file was causing hell with heroku---deleting it got me back to work.

Unfortunately, heroku's stack trace offers no real direction in sorting this out. There are a number of reasons you could see the "You are trying to install in deployment mode after changing your Gemfile" message---and, heroku offers nothing in helping you figure out why it is unhappy.