Update filesystem.md

Author: taylorotwell

filesystem.md

@@ -341,12 +341,12 @@ By default, this method will use your default disk. If you would like to specify
         'avatars/'.$request->user()->id, 's3'
     );
 
-If you are using the `storeAs` method, pass the disk name in a third argument of options array:
+If you are using the `storeAs` method, you may pass the disk name as the third argument to the method:
 
     $path = $request->file('avatar')->storeAs(
         'avatars',
         $request->user()->id,
-        ['disk' => 's3']
+        's3'
     );
 
 #### Other File Information