Update git submodules

* Update docs/submodules/usecase-ui.git from branch 'master'
  to 88f8607f42193606135191083b38b164991befa0
  - Merge "Migrate usecase-ui docs"
  - Migrate usecase-ui docs

    Merging this will create
    https://onap-usecase-ui.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: I2c2993ac3d0426b7bf81e16e3bf8ee61b6d00dff

diff --git a/docs/submodules/usecase-ui.git b/docs/submodules/usecase-ui.git
index 00ff3eb..88f8607 160000 (submodule)
--- a/docs/submodules/usecase-ui.git
+++ b/docs/submodules/usecase-ui.git
@@ -1 +1 @@
-Subproject commit 00ff3eb8ebd4ea4311832dbad9748f4ae2bd02b2
+Subproject commit 88f8607f42193606135191083b38b164991befa0