update README sample Gemfile to match gemspec
update README sample Gemfile to match gemspec

0x00evil/rails-1,inner-whisper/rails,custom-exposure/rails,capistrano/rails,annaswims/rails-1,YourCursus/capistrano-docker-cloud,ershad/capistrano-rails,banux/rails,YourCursus/capistrano-docker-cloud,januszm/capistrano-rails,k-yamada/capistrano-rails,kewaunited/rails-1,ipmobiletech/rails-1,mzaccari/rails,jongamboa17/rails