Fix incorrect function call in UPGRADING.md (#996)

Timothy Choi · bshaffer · commit 18dd55342803 · 2016-07-21T11:41:10.000-07:00
diff --git a/UPGRADING.md b/UPGRADING.md
@@ -175,7 +175,7 @@ $client->getAuth()
 **After**
 
 ```php
-$client->useDefaultApplicationCredentials();
+$client->useApplicationDefaultCredentials();
 $client->addScope('https://www.googleapis.com/auth/sqlservice.admin');
 ```
 
