upgrades: updating the proxy admin address was not emitting an event

Add AdminUpdated(address oldAdmin, address newAdmin) event whenever _setAdmin() is called

Author: abarmat

contracts/upgrades/GraphProxy.sol

@@ -23,7 +23,7 @@ contract GraphProxy is GraphProxyStorage {
         );
 
         _setAdmin(msg.sender);
-        upgradeTo(_impl);
+        _setPendingImplementation(_impl);
     }
 
     /**

contracts/upgrades/GraphProxyStorage.sol

@@ -45,6 +45,11 @@ contract GraphProxyStorage {
      */
     event ImplementationUpdated(address oldImplementation, address newImplementation);
 
+    /**
+     * @dev Emitted when the admin account has changed.
+     */
+    event AdminUpdated(address oldAdmin, address newAdmin);
+
     /**
      * @dev Modifier to check whether the `msg.sender` is the admin.
      */
@@ -72,6 +77,8 @@ contract GraphProxyStorage {
         assembly {
             sstore(slot, _newAdmin)
         }
+
+        emit AdminUpdated(_admin(), _newAdmin);
     }
 
     /**