Update git submodules

Update git submodules

* Update docs/submodules/ccsdk/platform/plugins.git from branch 'master'
  to 87d14cfc2cdcdfecbc75396d5347eae295bfb570
  - Merge "Migrate ccsdk-platform-plugins docs"
  - Migrate ccsdk-platform-plugins docs

    Merging this will create
    https://onap-ccsdk-platform-plugins.readthedocs.io
    This build will run in parallel
    to the current docs generation method
    until we are ready to cut over.

    Issue-ID: CIMAN-364
    Signed-off-by: Jessica Wagantall <jwagantall@linuxfoundation.org>
    Change-Id: I9aa49187b78337cbe5c3a787c75d52384b755857