Bump ruby patchlevel.
Updating to latest ruby-install (0.3.4)

- Extract ruby-install into /tmp, we don't need it hanging around in
  /usr/local once the executable is installed into /usr/local/bin
- Bump gems and cookbook dependencies to latest
- Update tests to latest stable rubies
- Bump kitchen-test OSs to latest stable versions
- Don't use `which` command in tests