Update git submodules

* Update docs/submodules/fuel from branch 'stable/danube'
  - f_tackerpluginbuild: Fix obsolete mitaka branch

    Tacker plugin defaults to using the "stable/mitaka" branch for
    the Tacker Horizon dashboard project, which was meanwhile nuked
    upstream.
    Switch to using the "mitaka-eol" tag instead.

    Change-Id: Iacec0ebdff7327bca9c84d9433790a04acd2dc4d
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 3098b32..956467b 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 3098b322a167f47b647ed078cc8fc746d4e5c3be
+Subproject commit 956467be603b7acadbc0e1912b84816bcbfd3850