Update submodules: plugins (new commits)

plugins:
    63ce3c2 Chris Smith <chris@dmdirc.com>
            Make plugin dependencies more flexible.

            Define a 'plugin' function to use in place of 'project' that
            will figure out where the plugin is living in the root gradle
            project.

            This allows the plugins to be included and built properly
            when they are in a submodule of either the client or the meta
            project.

            Gerrit: http://gerrit.dmdirc.com/4028

Change-Id: Iab53fed4a6805ead3dfc0daac71285e499117b7c