Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Committer promotion for Panos and Stamatis

    Panos and Stamatis have significantly contributed to Dovetail and
    projects utilized by Dovetail (e.g. Functest, Dovetail-webporal). Hence,
    I'd like to propose their promotion to committer.

    Panos:
    https://gerrit.opnfv.org/gerrit/#/q/owner:%22Panagiotis+Karalis+%253Cpkaralis%2540intracom-telecom.com%253E%22

    Stamatis:
    https://gerrit.opnfv.org/gerrit/#/q/owner:%22Stamatis+Katsaounis+%253Cmokats%2540intracom-telecom.com%253E%22

    Change-Id: Ibed0a5e3dc387d9de63c201db902133bd813c041
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 7694795..507a31e 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 76947950b0196367768068ae31f85ca175b672fb
+Subproject commit 507a31ea7ece33a887379db3fb836d5d5d0af582