update livestreamer-docs-url to reflect changes at docs.livestreamer.io
update livestreamer-docs-url to reflect changes at docs.livestreamer.io

chhe/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,chhe/livestreamer-twitch-gui,bastimeyer/livestreamer-twitch-gui,bastimeyer/livestreamer-twitch-gui,bastimeyer/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,streamlink/streamlink-twitch-gui,chhe/livestreamer-twitch-gui