bundle install gives undefined method `ruby' for #<Bundler::Dsl:0x00000001c4e1f8>

Version 1.2 of Gembundler introduced a ruby method to the dsl that allows you to specify the Ruby version your app should use.

It looks like the Gemfile you’re using was written for this new version, but the version of bundler you have doesn’t support the ruby method. You need to either install the latest bundler (gem install bundler should do it) or remove the line from your Gemfile.