Issue with Werkzeug on Windows

[bronikowski]

I've been helping someone with running your project on Windows, turns out a Werkzeug in a version stated in requirements.txt has a bug, could you bump it to Werkzeug==0.11.15 to avoid problems for other people?

Pull request fixing the issue, pallets/werkzeug#999

Sorry for not providing a patch, but it's just one line.