Add date to ChangeLog for 2.20.0 release
diff --git a/ChangeLog b/ChangeLog
index ab8267f..1d39172 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,6 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS 2.20.0 branch released xxxx-xx-xx
+= mbed TLS 2.20.0 branch released 2020-01-15
 
 Bugfix
    * Fix an incorrect size in a debugging message. Reported and fix