Update git submodules

* Update docs/submodules/fuel from branch 'stable/fraser'
  - [apt] Allow downgrades during APT operations

    Pinning certain packages (e.g. OVS) interfers with `dist-upgrade` if
    downgrades are not explicitly allowed.

    Change-Id: I0b001936e86228037c30f30812e32d6221ef458d
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 3472473..3fd2f2d 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 3472473854b2756cc070e71de9213c8c82f36f6e
+Subproject commit 3fd2f2d4dc1d46495cf02041f95450664390e09b