AppCode can't install gems.

gistfile1.txt

> gem install cocoapods --no-ri --no-rdoc --user-install

WARNING:  You don't have /Users/bgesiak/.gem/ruby/2.0.0/bin in your PATH,
    gem executables will not run.
Successfully installed i18n-0.6.5
Successfully installed multi_json-1.8.0
Successfully installed activesupport-3.2.14
Successfully installed nap-0.5.1
Building native extensions.  This could take a while...
ERROR:  Error installing cocoapods:
	ERROR: Failed to build gem native extension.

    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/include/ruby.h


Gem files will remain installed in /Users/bgesiak/.gem/ruby/2.0.0/gems/json-1.8.0 for inspection.
Results logged to /Users/bgesiak/.gem/ruby/2.0.0/gems/json-1.8.0/ext/json/ext/generator/gem_make.out