gm convert: FreeType library is not available after upgrading Heroku app to cedar 14

Question

I have a Node.js app running on heroku. It has been working fine until it was upgraded to cedar-14 recently. When the app is trying to write a text on an image using gm library, this error will occur:

"gm convert: FreeType library is not available (font.otf) [No such file or directory]."

If I run "heroku run gm -version", this is the output on the cedar-14 app:

Feature Support:

Thread Safe              yes
Large Files (> 32 bit)   yes
Large Memory (> 32 bit)  yes
BZIP                     yes
DPS                      no
FlashPix                 no
FreeType                 no
Ghostscript (Library)    no
JBIG                     yes
JPEG-2000                yes
JPEG                     yes
Little CMS               yes
Loadable Modules         no
OpenMP                   yes (201107)
PNG                      yes
TIFF                     yes
TRIO                     no
UMEM                     no
WMF                      no
X11                      yes
XML                      yes
ZLIB                     yes

It appears that freetype is disabled. This is the buildpacks I am using:

https://github.com/mcollina/heroku-buildpack-graphicsmagick
https://github.com/heroku/heroku-buildpack-nodejs

How to turn on freetype library on cedar-14 on heroku?