Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Merge "Add flake8 and yamllint tox environments and fix tox errors"
  - Add flake8 and yamllint tox environments and fix tox errors

    JIRA: SDNVPN-231

    This patch adds flake8 and yamllint tox environments. Furthermore, it
    fixes tox errors and applies general tox improvements.

    Change-Id: Id180695ef034562efb236932e6f783b0e91157c2
    Signed-off-by: Stamatis Katsaounis <mokats@intracom-telecom.com>

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 90780e7..2147aa5 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 90780e7d12b9003955cfbb8ff0155baf75b26323
+Subproject commit 2147aa5c54101fa3bf58f2551315fc454c7dc2b6