install gem before bundle installing

- this was forgotten in the 11.6.2 ohai symlink fix, and windows
  is broken (but nobody will care because /opt/chef/embedded/bin is in
  the windows PATH -- which is terrible and should get fixed)
- doing things two different ways on windows and unix is most
  likely bad and confusing
Merge pull request #101 from opscode/lcg/windows-gem-install-frist

install gem before bundle installing