Fixes load path issues with ruby-based git credential helpers

Otherwise, we get errors like this (with boxen, e.g.):

```
/opt/boxen/bin/boxen-git-credential:23:in `require': cannot load such file -- boxen/config (LoadError)
        from /opt/boxen/bin/boxen-git-credential:23:in `<main>'
Username for 'https://github.com':
```
Merge pull request #1609 from alindeman/patch-1

Fixes load path issues with ruby-based git credential helpers
.gitignore Gemfile.lock per previous commit

Gemfile.lock was removed in a previous commit, should be ignored so it doesn't get committed again.

https://github.com/imathis/octopress/commit/06c04397053e46fe02fcecce589a2de76d21e160
Merge pull request #1617 from nickhammond/patch-1

.gitignore Gemfile.lock per previous commit
Delete Gemfile.lock

Follow-up to #1617
Merge remote-tracking branch 'upstream/master'