Hi,

version 4.0.4 of xpra broke the builtin HTML server, causing
``--html=on`` to display the following error message:

2020-10-16 12:31:01,810 Error: cannot import websocket connection handler:
2020-10-16 12:31:01,810  No module named 'requests'
2020-10-16 12:31:01,810  the html server will not be available

The attached patch applies an upstream fix, until upstream releases a
new version.

Cheers,
Lars