Adding Bus Dispatcher to the Contracts reference

Noticed this was missing while I was reviewing things, so just adding it in.

contracts.md

@@ -103,6 +103,7 @@ Contract  |  Laravel 4.x Facade
 ------------- | -------------
 [Illuminate\Contracts\Auth\Guard](https://github.com/illuminate/contracts/blob/master/Auth/Guard.php)  |  Auth
 [Illuminate\Contracts\Auth\PasswordBroker](https://github.com/illuminate/contracts/blob/master/Auth/PasswordBroker.php)  |  Password
+[Illuminate\Contracts\Bus\Dispatcher](https://github.com/illuminate/contracts/blob/master/Bus/Dispatcher.php)  |  Bus
 [Illuminate\Contracts\Cache\Repository](https://github.com/illuminate/contracts/blob/master/Cache/Repository.php) | Cache
 [Illuminate\Contracts\Cache\Factory](https://github.com/illuminate/contracts/blob/master/Cache/Factory.php) | Cache::driver()
 [Illuminate\Contracts\Config\Repository](https://github.com/illuminate/contracts/blob/master/Config/Repository.php) | Config