Fixes for push.

@gaurave

Small fixes for push method. With these I was able to successfully push to Github, although I do note a bug that if you commit changes, close the client, reopen and attempt to push, the client claims that there are no commits to push. Not sure if this is some bug with the way the index is stored but not written to file?

Fixes:
- minor syntax fixes
- no need to return on completer.complete();
- progress(); is null and breaks everything when attempting to call
- attempt to add List<int> to a blob breaks everything, fixed with conversion to Uint8List