Fixed issues with completion in Storage.onStateChange stream
Fixed issues with completion in Storage.onStateChange stream

Fixes https://github.com/Janamou/firebase3-dart/issues/15

Janamou/firebase3-dart,Janamou/firebase3-dart,kevmoo/firebase-dart,kevmoo/firebase-dart,Janamou/firebase3-dart,kevmoo/firebase-dart