update mpd-git to latest and mpd-20 to 0.20.11

ver 0.20.11 (2017/10/18)

• storage
  • curl: support Content-Type application/xml
• decoder
  • ffmpeg: more reliable song duration
  • gme: fix track numbering
• improve random song order when switching songs manually
• fix case insensitive search without libicu
• fix Unicode file names in playlists on Windows
• fix endless loop when accessing malformed file names in ZIP files