Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - lib.sh: Fix `modprobe -f` on Ubuntu

    For some reason, `modprobe -f` for a clean nbd module (from vanilla
    Ubuntu) fails with exec format error randomly, while a simple
    `modprobe` works.

    Change-Id: I79785e510cab757e2482baf442054be984c24019
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 510a5fe446dea8513060813794c99e856eff1845)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 5f1f119..4874ba3 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 5f1f119d8043793821b89e61a0830ce8505635ab
+Subproject commit 4874ba30071630c6b96eb6ea912a4fe047e0d93c