Update submodules: plugins (new commits)

plugins:
    266876c Chris Smith <chris@dmdirc.com>
            Plugin support for FrameContainer changes.

            Depends-On: I3b95185db3f7e6ef09a6c4f91cd28c88d2c601ba
            Gerrit: http://gerrit.dmdirc.com/3106

Change-Id: Ie9b1566426d591d10e9d0e326b4cdb8fe5bd532c