Cloud 9 ImageMagick Error

error.log

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    /usr/local/rvm/rubies/ruby-2.1.2/bin/ruby extconf.rb 
checking for gcc... yes
checking for Magick-config... no
checking for pkg-config... yes
Package MagickCore was not found in the pkg-config search path.
Perhaps you should add the directory containing `MagickCore.pc'
to the PKG_CONFIG_PATH environment variable
No package 'MagickCore' found
checking for outdated ImageMagick version (<= 6.4.9)... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=/usr/local/rvm/rubies/ruby-2.1.2/bin/ruby

extconf failed, exit code 1

Gem files will remain installed in /usr/local/rvm/gems/ruby-2.1.2/gems/rmagick-2.15.4 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.1.2/extensions/x86_64-linux/2.1.0/rmagick-2.15.4/gem_make.out
An error occurred while installing rmagick (2.15.4), and Bundler cannot continue.
Make sure that `gem install rmagick -v '2.15.4'` succeeds before bundling.

Do you know how to fix this error?