Replaced gitignore file with content as in all other barclamps

I renamed the gitignore within
https://github.com/tboerger/barclamp-git/commit/7ffc9d91df8441b46b863e2ba4fd0a310f354122 wrong. Simply renamed it to .gitignore
now.
Merge pull request #53 from tboerger/feature/gitignore-replace

Replaced gitignore file with content as in all other barclamps