Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - MaaS: Fix missing service.maas.cluster.single inc

    Upstream change [1] made the inclusion of service.maas.cluster.single
    mandatory by using some default reclass definitions which we don't
    override explicitly.

    [1] https://github.com/salt-formulas/salt-formula-maas/commit/
        ce118a238bae4bcf19d2f10bca591a40405f7c3c

    Change-Id: I5746b6906b341a7257e0cd2b4b0bed8ea25840f4
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 4b2dfa552656def5f56a48229705e79c5c7bcfca)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index a9f57c2..4a0224d 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit a9f57c2149731cad16ce92d7eca8ade12fb9f003
+Subproject commit 4a0224d6a15500d560fc2d708b0190d7027f1f37