Fixed Firebase dependency in Bower.json

The Firebase dependency in the `bower.json` file was just set to `*`, which is generally a bad idea and also screwed things up a bit when Firebase updated to 2.0.x. In general, `*` shouldn't be used as major version changes are expected to have breaking changes. This reverts the library back to `1.1.x` and fixes #19.

cc/ @chuckh