A bug when generating plantuml URL on windows platform

This is caused by the difference of the implements of os.path.join on Linux and windows.

from plantumlcli import RemotePlantuml

if __name__ == "__main__":
    r = RemotePlantuml.autoload()
    print(r._RemotePlantuml__request_url(os.path.join('123', 'sdkfjl')))

It will print http://www.plantuml.com/plantuml/123%5Csdkfjl on windows, while this is a wrong url.