Allow '.ruby-version' file into repo.
Specify 1.9.3-p429 in repo & in Gemfile for Heroku.

The most recent Ruby security patch announcement states that ruby 1.9.2
is still vulnerable, so specifying the current 1.9.3 patchlevel.

Bundler doesn't allow patchlevels to be included in the Gemfile's
ruby directive, but Heroku's version of 1.9.3 is the current one.
Merge pull request #51 from railsbridge-boston/heroku-repo-ruby

Bump Ruby version in repo to latest 1.9.3.

[Actual bump on Heroku will happen on next deploy.]