Bug when fetching modules from forge using 'puppet module install'

I had an issue where I was systematically getting the latest version of modules even if I specified earlier versions in my Puppetfile. Looks like there was a problem with the way `puppet module install` was getting invoked when no vendored cached versions was found locally: no `--version` parameter was being used.

This change fixed that issue for me. Let me know if there is something I missed.