Update submodules: util (new commits)

util:
    18b3add Chris Smith <chris@dmdirc.com>
            Add an alternative formatter.

            Formatting durations as 'XX:YY' is fairly common and repeated
            in nearly all the nowplaying sources. Make a util method instead.

            Gerrit: http://gerrit.dmdirc.com/3986

Change-Id: I2992c2d10a98bb2e8d55afb73fa5abdd90d0384c