Fix whitespaces at last line.

Author: josemacassan

tests/integration/test_integration_response_headers.py

@@ -2,4 +2,4 @@
 def test_x_served_by(api):
     response = api._rest.get(url=api.admin_api_url + '/accounts')
     assert response.status_code == 200
-    assert "X-Served-By" not in response.headers
+    assert "X-Served-By" not in response.headers