Update git submodules

* Update plugins/singleusergroup from branch 'stable-2.15'
  to 0ffbdf1e5c3daa9d118ee9f53d5c00497cff6454
  - Bazel: Reformat BUILD file with buildifier 0.17.2
    
    Change-Id: I0aac4a7b965b5bce69e8a5370f11d0dda4b27667
    
diff --git a/plugins/singleusergroup b/plugins/singleusergroup
index 64032d7..0ffbdf1 160000
--- a/plugins/singleusergroup
+++ b/plugins/singleusergroup
@@ -1 +1 @@
-Subproject commit 64032d745bf818201f0d41dfb8a355d15e1bdc9f
+Subproject commit 0ffbdf1e5c3daa9d118ee9f53d5c00497cff6454