Update bower.json

Fix for error
```
bower validate      1.1.3 against git://github.com/firebase/firebase-bower.git#*
bower checkout      firebase-import#master
bower invalid-meta  firebase-import is missing "main" entry in bower.json
bower invalid-meta  firebase-import is missing "ignore" entry in bower.json
bower ENORESTARGET  Tag/branch firebase does not exist
```