Redirect to file: broken on windows.

[jschwartzentruber]

When launching ffpuppet on windows with -u, the redirect is broken:

set DEBUG=1
python -m ffpuppet \build\firefox.exe -u tc.html
...
D ffpuppet [2017-09-07 14:46:21] sending response with redirect url: 'file://////C:/Users/user/Desktop/tc.html'

The browser doesn't resolve the file: url. Entering it manually as file://C:/Users/... works fine.

[tysmith]

Fixed by commit ab8fc75.