$ ruby app.rb
/home/action/.parts/packages/ruby2.1/2.1.1/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- gmail-ruby (LoadError)
        from /home/action/.parts/packages/ruby2.1/2.1.1/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from app.rb:2:in `<main>'