[PATCH] Generator 'gem' command doesn't accept versions

In master, the gem command of generators will append to the Gemfile an unescaped version string. For example, with this command:

gem 'rspec', '>=2.0.0.a5'

The Gemfile will look like so at the end:

gem "rspec", >=2.0.0.a5

The attached patch fixes this behavior and adds tests both for the version escaping as well as testing to make sure each gem gets its own line.