Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "states: maas: Stop using maas-stable PPA"
  - states: maas: Stop using maas-stable PPA

    Currently, Xenial repos provide MaaS 2.2.x, while the PPA bumped it
    to 2.3.x. Since we switched to 2.3, we observed a rare wrongful state
    transition from 'Deploying' back to 'Ready'.
    Drop the PPA, falling back to 2.2 from mainline distro repos.

    JIRA: FUEL-312

    Change-Id: I3daa118059f37cbeca076da685661c28f3a28a97
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 24dad46..c976700 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 24dad46d51e6740400effd037f14d99defc5eafd
+Subproject commit c976700c1e8702881f67f3306a67d56c9f78c327