Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "[apt-mk] Switch back to nightly"
  - [apt-mk] Switch back to nightly

    Revert "salt: Use apt-mk 'stable' distribution"
    Revert "reclass: apt_mk_version: stable"

    This reverts commit d1b6119e288a31e015573363ce77790fec8684df.
    This reverts commit 4563ea7d62238e8273d840a8d9c6c1e179ca584e.

    Change-Id: I383db1f78a087045086096cbc674260b985fd913
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 4658acf..6357d86 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 4658acf952c263b2c402c43ac7cd90a41d4272fa
+Subproject commit 6357d861c2f7c69c1486a40a81d24d7dda66eba8