Update git submodules

* Update plugins/singleusergroup from branch 'stable-2.16'
  to 8a81e853a07b1bbd28766793e31d44787dfde1f6
  - Fix the testAllNumericUserGroup all-numeric username
    Bug: Issue 11498
    Change-Id: Iee6dc050f8d1e97920c3e105af7bd2a69479dcea
  - Merge branch 'stable-2.15' into stable-2.16
    * stable-2.15:
      Test all-numeric username
    Change-Id: Ie659c4e19b9258dcb5b4ada96305d47b591cd5b7
  - Test all-numeric username
    Verify that a username with all numbers works as expected
    and generates an equivalent group associated with it.
    Change-Id: Ie98181fdecbf196c320b8b9d0ca0c7bd88b0d238
diff --git a/plugins/singleusergroup b/plugins/singleusergroup
index ae9a9ab..8a81e85 160000
--- a/plugins/singleusergroup
+++ b/plugins/singleusergroup
@@ -1 +1 @@
-Subproject commit ae9a9ab370d8026ad809a73b4dae3fb7d79ad8a4
+Subproject commit 8a81e853a07b1bbd28766793e31d44787dfde1f6