RC version fix.

Currently 'beta.3' is preferred to 'RC3' when newest prerelease is requested. That occurs because rubygems compares versions case-sensitively on part-by-part basis and uppercase 'RC' is less than lowercase 'beta' for the purposes of this comparison.

Could you merge this PR and release as soon as possible? It's inconvenient to specify version manually, and anyone not aware of this issue would be somewhat puzzled by `undefined method generators_path` on attempt to generate anything.