Bug in Flask embed example?

I tried testing the Flask embedding example (https://github.com/bokeh/bokeh/blob/0.13.0/examples/howto/server_embed/flask_embed.py). However, it didn’t work for me until I added 127.0.0.1:8000 to the allow_websocket_origin list. Is this a bug? If so, I can submit a PR to fix.

Brad