Update submodules: installer (new commits)

installer:
    291a6b1 Chris Smith <chris@dmdirc.com>
            Add script to submit plugins to the addons site.

            This mirrors the functionality in the build-plugins.xml ant project
            in the main repo, but as it's not using ant is an awful lot nicer
            and more sane.

            We'll use this to submit plugins from teamcity builds.

            Gerrit: http://gerrit.dmdirc.com/3355

Change-Id: I911f441f1d1a8e0c15a9bbaeed2c1336b46cb634