Update submodules: plugins (new commits)

plugins:
    956e226 Chris Smith <chris@dmdirc.com>
            Remove MessageSinkManager singleton.

            Depends-On: Iaafcea914d16f33ce98c331084cd3e9c8fdbbeda
            Gerrit: http://gerrit.dmdirc.com/2822

Change-Id: I0daee3224e8c4e6de37f3998d20a57f47d1bb3e7
Remove MessageSinkManager singleton.

Change-Id: Iaafcea914d16f33ce98c331084cd3e9c8fdbbeda
Depends-On: I1cd8a5676beab1f3aba7f62b064dd5b2c2ce0f61
Reviewed-on: http://gerrit.dmdirc.com/2821
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>