Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Adapting local docs build and remove build warnings

    The OPNFV docs project will remove its submodules and enable local docs
    builds. This patch prepares the Dovetail repo according to the official
    transition guide:

    https://docs.opnfv.org/en/latest/how-to-use-docs/local-build-transition.html

    This patch also applies syntactical changes which eliminate the sphinx
    doc build warnings.

    Change-Id: Ief8fd2d1c3e39b232d214a9ab392879ee4a492c8
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 60f1c35..a18e2b0 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 60f1c35c294d5d94a862db348315f8f3b9f870ba
+Subproject commit a18e2b0d45c631709e457530f6f9d0b52f552156