Update submodules: plugins (new commits)

plugins:
    a574db3 Greg Holmes <greg@dmdirc.com>
            Fix DCC Plugin show config.

            Fixes-Issue: CLIENT-440
            Gerrit: http://gerrit.dmdirc.com/3156

Change-Id: Ib3c81a98cbd92c1da6f1ef9643c297a91cbb394e