Add missing override annotation

Author: kevinsawicki

app/src/main/java/com/github/mobile/ui/gist/GistsViewActivity.java

@@ -193,6 +193,7 @@ public void startActivity(Intent intent) {
             super.startActivity(intent);
     }
 
+    @Override
     protected FragmentProvider getProvider() {
         return adapter;
     }