RailsBricks 3.1.2 brings support for Ruby 2.2.0. Now, you can build apps using Ruby 2.0.0, 2.1.5 or 2.2.0.
Note that Rails 5 will only support Ruby 2.2+. From Rails official blog:
Rails 5.0 will target Ruby 2.2+ exclusively. There are a bunch of optimizations coming in Ruby 2.2 that are going to be very nice, but most importantly for Rails, symbols are going to be garbage collected. This means we can shed a lot of weight related to juggling strings when we accept input from the outside world. It also means that we can convert fully to keyword arguments and all the other good stuff from the latest Ruby.
It is therefore strongly advised to start your new RailsBricks projects with Ruby 2.2.0.
Away with the old!