Update submodules: plugins (new commits)

plugins:
    db60c28 Chris Smith <chris@dmdirc.com>
            Gradle version bump

            Gerrit: http://gerrit.dmdirc.com/3897

Change-Id: I2479fe82cf3533a875ad19e0c438756397fdb279
Gradle version bump

Change-Id: I3083c2e0ffc75019f752966e5a95dab138c82c3d
Reviewed-on: http://gerrit.dmdirc.com/3898
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager