Fixes for heroku-push on Windows

* https://github.com/andriykohut/tutorial/commit/76b2d89b6d1ec52fe434a7fae0ca57946d0cd19c#diff-bcdcc71d7dab57472393a413b9f8293dR144 - fork of https://github.com/ddollar/heroku-push, fixed issue with window paths (https://github.com/DjangoGirls/tutorial/issues/143)

* https://github.com/andriykohut/tutorial/commit/76b2d89b6d1ec52fe434a7fae0ca57946d0cd19c#diff-bcdcc71d7dab57472393a413b9f8293dR148 - `heroku-push` requires existing git repo to use .gitignore (Proof: https://github.com/ddollar/heroku-push/blob/master/lib/push/heroku/command/push.rb#L82), without it it will just push everything in current directory.