Update submodules: plugins (new commits)

plugins:
    6dc22a2 Chris Smith <chris@dmdirc.com>
            Unused field.

            Gerrit: http://gerrit.dmdirc.com/3648

    52f02f4 Chris Smith <chris@dmdirc.com>
            Introduce a DcopExecutor, deprecated static junk.

            Gerrit: http://gerrit.dmdirc.com/3647

Change-Id: I8611c917217336ddbcc8ff3f66d330d733da60f5