Update git submodules

* Update plugins/plugin-manager from branch 'master'
  to d486f1edac54c63c46f92c93fa15958f89cfe60f
  - Merge branch 'stable-2.16'
    
    * stable-2.16:
      Set next version to 3.1
    
    Change-Id: I71973fc0b2e2764997f7007beabb2d257ca3f6eb
    
  - Set next version to 3.1
    
    Next forthcoming Gerrit version is 3.1 and thus the plugin-manager
    should return master plugins when the version string starts with
    3.1 *ONLY*.
    
    Bug: Issue 11880
    Change-Id: I49e193c75d2937b2ddb8dd67c1d84bf8b4e52bb9
    
diff --git a/plugins/plugin-manager b/plugins/plugin-manager
index c921234..d486f1e 160000
--- a/plugins/plugin-manager
+++ b/plugins/plugin-manager
@@ -1 +1 @@
-Subproject commit c921234cec4c0d058b35a8d117f55fce4d4c5e65
+Subproject commit d486f1edac54c63c46f92c93fa15958f89cfe60f