Ruby and Rail Application Error when Running Bundle install

I am following a heroku tutorial where I created my rails app. I was asked to use Heroku to get my app live online. But I have troubled to run the command Bundle install. It keeps giving me an error.

I tried to re-install Rail Bundler on my Terminal, but it shows me this error at the terminal:

/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
extconf.rb
creating Makefile

make "DESTDIR="
compiling generator.c
In file included from generator.c:1:
In file included from ./../fbuffer/fbuffer.h:5:
In file included from
/Applications/http://ift.tt/2lcpfyW:
/Applications/http://ift.tt/2jPJoxO:
fatal error: 'ruby/config.h' file not found
#include "ruby/config.h"
         ^
1 error generated.
make: *** [generator.o] Error 1


Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/json-1.8.1 for
inspection.
Results logged to
/Library/Ruby/Gems/2.0.0/gems/json-1.8.1/ext/json/ext/generator/gem_make.out

An error occurred while installing json (1.8.1), and Bundler cannot
continue.
Make sure that `gem install json -v '1.8.1'` succeeds before bundling.