Bump Celluloid to latest pre-release

This will fix the inability to run finalizers when using TaskThread for the task class. This will stop the scary error output when shutting down applications using Ridley and also prevent applications from hanging for 10 seconds while Celluloid attempts to shut down all of it's actors.

Additionally *all* finalizers should *only* make asynchronous calls to other actors inside of their finalizers.

I'm not sure when we'll be seeing a full release of Celluloid, so we'll have to settle for locking to the pre-release for now.

/cc @sethvargo @ivey