Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - [patch] Rebase keyserver patch for disabled repos

    Rebase patch on top of upstream commit [1].
    [1] https://github.com/salt-formulas/salt-formula-linux/commit/45cf452d

    Change-Id: Id44eab58150ff69140f630352a299633cdb4f4ac
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index c415687..c52837f 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit c4156877d3f3f4f7efbca6e129bbeafdbe877d22
+Subproject commit c52837f7d28b7c0f231be2b0215a7035b26ae302