Update submodules: plugins (new commits)

plugins:
    e88f821 Greg Holmes <greg@dmdirc.com>
            Remove warnings in plugins

            Gerrit: http://gerrit.dmdirc.com/3178

Change-Id: I27598e0ed04a16a79a7d5b88bacbc0ac6a52e0b9

modules/plugins

@@ -1 +1 @@
-Subproject commit 2049c56405703571ecb7ea77bd98a373a844fd7e
+Subproject commit e88f8215d9aa0429874c358f847cee9ded36f58c