fix mm.logout docs
fix mm.logout docs

jimyx17/gmusic,simon-weber/Unofficial-Google-Music-API,dvirtz/gmusicapi,dvirtz/gmusicapi,peetahzee/Unofficial-Google-Music-API,thebigmunch/gmusicapi,nvbn/Unofficial-Google-Music-API,TheOpenDevProject/gmusicapi,simon-weber/gmusicapi,tanhaiwang/gmusicapi