Update submodules: plugins (new commits)

plugins:
    e37cff3 Greg Holmes <greg@dmdirc.com>
            Remove unused field.

            Gerrit: http://gerrit.dmdirc.com/3325

    a801f8a Greg Holmes <greg@dmdirc.com>
            Use active window frame manager.

            Gerrit: http://gerrit.dmdirc.com/3323

Change-Id: Ieaede9f654371f80124ed499b90ec23de3ad1066