Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [patch] MaaS: Switch to upstream fabric/vlan mgmt

    Obsolete our out of tree patch in favor of upstream mechanisms for
    creating fabrics/VLANs/subnets.

    Change-Id: I57d6d59764a825b428f423d48c5d90af7f2e676f
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index b52c4df..3831d53 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit b52c4df4061fd7a51aad94f144bb1326fa8a8b5a
+Subproject commit 3831d538436cbf7c033b560b76f554a1dfe28a4c