Update to tests, AND a fix for addingChildLayers.
Merge branch 'master' of https://github.com/SpatialServer/Leaflet.MapboxVectorTile

# By Nicholas Hallahan
# Via Nicholas Hallahan
* 'master' of https://github.com/SpatialServer/Leaflet.MapboxVectorTile:
  version bump
  wrote mutex test, commented it out, not working yet. come back to later.
  build didn't get into commit
  bad reference to _map
  mutex toggle