Update git submodules

* Update docs/submodules/fuel from branch 'stable/fraser'
  - [docs] Update documentation for Fraser-6.1

    Change-Id: Ic5e71c0ce2bcfd9d01f07fff017aac8019793527
    Signed-off-by: Charalampos Kominos <Charalampos.Kominos@enea.com>
    (cherry picked from commit 3f78ef6a2b3cbd7fb509ec12d694b35ff6aad26d)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 504f00b..b1f2be6 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 504f00b570186664be8f16a52aa19075f9b25841
+Subproject commit b1f2be631eb5c2622beae350b992aa034885cd7c