Update docs of FacebookBatchRequest::add method

Author: teldosas

docs/reference/FacebookBatchRequest.md

@@ -62,9 +62,9 @@ Since the `Facebook\FacebookBatchRequest` is extended from the [`Facebook\Facebo
 ### add()
 ```php
 public add(
-  array|Facebook\FacebookBatchRequest $request,
-  string|null $name
-  )
+    array|Facebook\FacebookBatchRequest $request,
+    string|null $name
+)
 ```
 Adds a request to be sent in the batch request. The `$request` can be a single [`Facebook\FacebookRequest`](FacebookRequest.md) or an array of `Facebook\FacebookRequest`'s.