Log Message:
Updated musicpd to 0.20.8.

ver 0.20.8 (not yet released)
* output
  - osx: fix build failure due to missing "noexcept"
* playlist
  - m3u: support MIME type `audio/mpegurl`
* fix build failure with GCC 4.x

ver 0.20.7 (2017/05/15)
* database
  - simple: fix false positive directory loop detection with NFS
* enforce a reasonable minimum audio_buffer_size setting
* cap buffer_before_play at 80% to prevent deadlock
* fix random crashes when compiled with clang