Update MorphToMany.php

Changes the morphType value saved to the database so that it does not include slashes "\\" when using a full namespace like, ie $this->has_many('Wpb\AdminModule\Models\RMMatrix'... for some reason when using mysql it now always returns a empty array if there are any slashes in a query value. Replacing the "\" in the db stored value allows the full namespace to be used... more details are at https://github.com/laravel/framework/issues/4006#issuecomment-42623621