Update git submodules

* Update ChronoSync from branch 'master'
  to 5f408ae7f52f2fb792c65db733c80c6d4d5ecf48
  - build: align minimum build dependencies with ndn-cxx
    
     * Recommend gcc >= 7.4.0
     * Require clang >= 4.0, or Xcode >= 9.0 on macOS
     * Silence an ABI-related diagnostic message from gcc on armv7
     * Update Travis CI job matrix
    
    Refs: #5087, #5106
    Change-Id: I71aef00147a7ad93b537904bb309745fed77f509
    
diff --git a/ChronoSync b/ChronoSync
index cc6f67c..5f408ae 160000
--- a/ChronoSync
+++ b/ChronoSync
@@ -1 +1 @@
-Subproject commit cc6f67cec9ef196cb776b44cf2a1a3d130385a5d
+Subproject commit 5f408ae7f52f2fb792c65db733c80c6d4d5ecf48