MPD issue with Bubbleupnp

[VyacheslavS]

@irobot

This is unusual but the version of mpd that runs on Volumio is rather old by now
(0.20.18, Feb 2018) and it had many improvements to http streaming since.

MPD can be updated: MPD 0.21.16 for Volumio (arm, armv7 and x86)