clean up browser check and run windows integrity on py3.6

.github/workflows/windowstests.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v1
         with:
-          python-version: 3.5
+          python-version: 3.6
       - name: Set up Node
         uses: actions/setup-node@v1
         with:

jupyterlab/browser_check.py

@@ -51,7 +51,7 @@ class LogErrorHandler(logging.Handler):
         # These occur when we forcibly close Websockets or
         # browser connections during the test.
         # https://github.com/tornadoweb/tornado/issues/2834
-        if hasattr(record, 'exc_info') and isinstance(record.exc_info[1], StreamClosedError):
+        if hasattr(record, 'exc_info') and not record.exc_info is None and isinstance(record.exc_info[1], StreamClosedError):
             return
         return super().filter(record)