Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - lib.sh: Limit envsubst to certain variables

    This will prevent envsubst from expanding the SALT_REPO local
    variable in user-data.template.

    Change-Id: Idcc3ea827293ac0d3b4059776f90bbbcf807daec
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 06c6694..3a76d07 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 06c66940cad08ae875bba5791822e8895468780b
+Subproject commit 3a76d07dbd409b781abdb8520f55a1b20edf07db