Fix abort gitlab:app:check

When the file that pointed git bin_path in gitlab.yml dose'nt exist,
bundle rake gitlab:app:check would be aborted.

refs #4205

Newer output is like following
```
Your git bin path is "/usr/local/bin/git/a"
Git version >= 1.7.10 ? ... no
  Try fixing it:
  Update your git to a version >= 1.7.10 from Unknown
  Please fix the error above and rerun the checks.
```