Don't run bundle install as part of creating a rails app

- Bundle is ran afterwards, so we avoid installing gems twice
- We also need to update gems (such as exejcs-2.0.2) so the second bundle install fails
freeze version of execjs

- Rubinius build is currently failing with the latest version of execjs
- Execjs is used for tests written in coffee script
Merge pull request #219 from jordi-pivotal/fix-rubinius

Fix rubinius test failures