Update codebase to L5.4 (#367)

config/broadcasting.php

@@ -11,9 +11,10 @@ return [
     | framework when an event needs to be broadcast. You may set this to
     | any of the connections defined in the "connections" array below.
     |
+    | Supported: "pusher", "redis", "log", "null"
+    |
     */
-
-    'default' => env('BROADCAST_DRIVER', 'pusher'),
+    'default' => env('BROADCAST_DRIVER', 'null'),
 
     /*
     |--------------------------------------------------------------------------
@@ -44,6 +45,10 @@ return [
             'driver' => 'log',
         ],
 
+        'null' => [
+            'driver' => 'null',
+        ],
+
     ],
 
 ];