Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Nominating Nikos Karandreas as SDNVPN committer

    I would like to nominate Nikos Karandreas as SDNVPN committer due to
    his wide knowledge and working experience with SDNVPN project. He is
    currently working to incorporate HEAT templates for BGPVPN orchestration
    and fixing up CI issues.

    His contributions are: https://gerrit.opnfv.org/gerrit/#/q/owner:%22Nikos+Karandreas+%253Cnick%2540intracom-telecom.com%253E%22+project:sdnvpn

    Change-Id: Ibe7fd66573f8e0beeb073e3f3cf0d4907c671d0f
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>