Updated bower.json - because the dependencies for leaflet.markerclustere...

"bower install" no longer works because the "leaflet.markerclusterer" project doesn't have any tags (I'm not sure if the tags were removed, but there is only a single branch: master, so the bower install portion of this project failed until I removed the 0.4 version from the bower.json).

I've also created a 0.7.3 version of this project in my fork for reference.