Fix Mail::queue issue

The serializer seems to be at fault here. A suggestion here,  laravel/framework#3734 , was to use `Queue:push` with `Mail::send` to create a more reliable function. Testing on my setup works fine and I don't see a reason it wouldn't work on another setup. 

This should solve [Sentinel issue#38](https://github.com/rydurham/Sentinel/issues/38)