Update git submodules

* Update docs/submodules/appc.git from branch 'master'
  to 57293e84a0aa7405c9688448483d811d707e199a
  - Test coverage in MetricRegistryImpl
    
    Added test coverage for MetricRegistryImpl
    
    Issue-ID: APPC-1478
    Change-Id: I91eff5418ec14d294fa80af3d6d7025338b82072
    Signed-off-by: Joss Armstrong <joss.armstrong@ericsson.com>
    
diff --git a/docs/submodules/appc.git b/docs/submodules/appc.git
index 6c2b81d..57293e8 160000
--- a/docs/submodules/appc.git
+++ b/docs/submodules/appc.git
@@ -1 +1 @@
-Subproject commit 6c2b81d1d39e734435cabd66518fff26bcd49aec
+Subproject commit 57293e84a0aa7405c9688448483d811d707e199a