Error from AppVeyor:
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\appveyor\\AppData\\Local\\Temp\\1\\pip-98mhaiaq-uninstall\\python36\\scripts\\pip.exe'

Solution can be found here https://pythonhosted.org/CodeChat/appveyor.yml.html
Use python -m pip install -U pip