Fix Gemfile with https for github

GitHub needs https :
```
$ bundle install
Fetching http://github.com/hh/em-winrm.git
error: RPC failed; result=22, HTTP code = 405
fatal: The remote end hung up unexpectedly
Git error: command `git clone 'http://github.com/hh/em-winrm.git'
"/home/meister/.rbenv/versions/1.9.2-p320/lib/ruby/gems/1.9.1/cache/bundler/git/em-winrm-92096f33e44f28378ca608a4d2323b9abc51cf3a" --bare --no-hardlinks` in directory
/space/ci/veewee has failed.
```