Update submodules: util (new commits)

util:
    f6b5653 Chris Smith <chris@dmdirc.com>
            Make ReverseFileReader autocloseable.

            Because why not?

            Gerrit: http://gerrit.dmdirc.com/4048

Change-Id: Ie09b7dd2e9481235306a38b053a71ad1db8f7d09