Update git submodules

* Update docs/submodules/appc.git from branch 'master'
  to 18e906c444f39b4df933ae9570dc4ee5df5e36df
  - Correct line indent spacing

    The indent spacing was incorrectly changed to 2 spaces
    instead of 4 by https://gerrit.onap.org/r/#/c/78396/
    The incorrect spacing change was causing merge conflicts
    in another commit.

    Change-Id: I6693b3bfaa5685318c8ada5d7984235c788b9504
    Signed-off-by: Patrick Brady <patrick.brady@att.com>
    Issue-ID: APPC-1420

diff --git a/docs/submodules/appc.git b/docs/submodules/appc.git
index dfa1071..18e906c 160000 (submodule)
--- a/docs/submodules/appc.git
+++ b/docs/submodules/appc.git
@@ -1 +1 @@
-Subproject commit dfa107152577e88749eb5344a861279d09499ad4
+Subproject commit 18e906c444f39b4df933ae9570dc4ee5df5e36df