Update git submodules

* Update ChronoSync from branch 'master'
  to 4db56c8e3f8607c9ff47d81e52f14a4fae011075
  - ci: add gcc-9 to Travis CI build matrix
    
    Change-Id: I37c8399650666a4682fda4229c3ded2dca8e5ebd
    
diff --git a/ChronoSync b/ChronoSync
index d057cf1..4db56c8 160000
--- a/ChronoSync
+++ b/ChronoSync
@@ -1 +1 @@
-Subproject commit d057cf196981b9ea3ac1edd8b4baa27658d830e6
+Subproject commit 4db56c8e3f8607c9ff47d81e52f14a4fae011075