Improve the code example in testing docs

docs/testing.rst

@@ -333,7 +333,7 @@ happen.  With Flask 0.4 this is possible by using the
 
     with app.test_client() as c:
         rv = c.get('/?tequila=42')
-        assert request.args['tequila'] == '42'
+        assert flask.request.args['tequila'] == '42'
 
 If you were to use just the :meth:`~flask.Flask.test_client` without
 the ``with`` block, the ``assert`` would fail with an error because `request`