Different nc(1) implementations will use different flags, as highlighted
in #576. This environment variable allows one to pass any option to the
nc binary.
As of v0.21.4 version of the MPD command protocol, it seems that the
`version` command is not valid:
$ echo version | /bin/nc localhost 6600
OK MPD 0.21.4
ACK [5@0] {} unknown command "version"
Use `stats` instead.
https://www.musicpd.org/doc/html/protocol.html#querying-mpd-s-status