Bug 1373444 - Fix typo in wpt harness, r=maja_zf

MozReview-Commit-ID: 3x0JxmvRAvV

--HG--
extra : rebase_source : e0317356e1c6f27433b6347258a9e45b92fc4298

testing/web-platform/tests/tools/wptrunner/wptrunner/executors/executormarionette.py

@@ -462,7 +462,7 @@ class MarionetteRefTestExecutor(RefTestExecutor):
             super(self.__class__, self).teardown()
         except Exception as e:
             # Ignore errors during teardown
-            self.logger.warning(traceback.traceback.format_exc(e))
+            self.logger.warning(traceback.format_exc(e))
 
     def is_alive(self):
         return self.protocol.is_alive