Update git submodules

* Update docs/submodules/fuel from branch 'stable/danube'
  - docs: Refresh reference for Danube 2.0

    Change-Id: If786099581cf8bf685cc2076c21d4c3041610bf7
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 09c1ca15f2b01393d808453c9c2aeef1ec5895f5)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 040614e..a77f057 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 040614e651db4236e303d02eb9516f8648a74cf9
+Subproject commit a77f0573946c9b12b9665b19216202f1f740f084