Update README.md (#813)

Make consistent with changes

Author: rogerhu

gcm/README.md

@@ -77,7 +77,7 @@ public void onCreate() {
             //...
             .build();
     Parse.initialize(configuration);
-    ParseGCM.register(this, gcmSenderId);
+    ParseGCM.register(this);
 }
 ```
 The sender ID should be all numbers. It is obtained via the Firebase console.
@@ -93,4 +93,4 @@ If you need to customize the notification that is sent out from a push, you can
 
     This source code is licensed under the BSD-style license found in the
     LICENSE file in the root directory of this source tree. An additional grant
-    of patent rights can be found in the PATENTS file in the same directory.
+    of patent rights can be found in the PATENTS file in the same directory.