Update git submodules

* Update docs/submodules/appc.git from branch 'master'
  to 6c2b81d1d39e734435cabd66518fff26bcd49aec
  - Test coverage in MessageAdapterImpl
    
    Added test cases for untested portions of code
    
    Issue-ID: APPC-1481
    Change-Id: Id61ec5c5824c3d9fecbfb83d47bfa0164ae96759
    Signed-off-by: Joss Armstrong <joss.armstrong@ericsson.com>
    
diff --git a/docs/submodules/appc.git b/docs/submodules/appc.git
index 8c0057e..6c2b81d 160000
--- a/docs/submodules/appc.git
+++ b/docs/submodules/appc.git
@@ -1 +1 @@
-Subproject commit 8c0057e9f185d0ca632c2072a182cbee46f92c50
+Subproject commit 6c2b81d1d39e734435cabd66518fff26bcd49aec