Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [MaaS] Arch-qualify Saltstack repo for Xenial

    Previous changes altering Saltstack repo URL did not add an
    arch qulification, leading to APT trying to fetch the repo metadata
    for the current system architecture, failing on arm64 systems.

    Change-Id: Ibe32d90a8da2e04563ac9170939de92a4db233fd
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index e5d54bf..24572d5 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit e5d54bfdddc6b501e74a7d13be19e69724e20adb
+Subproject commit 24572d5956da62b1492c053cac82037b266a6739