Update version to 1.3.21
diff --git a/ChangeLog b/ChangeLog
index f383ae5..240bf84 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,6 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS 1.3.21 branch released xxxx-xx-xx
+= mbed TLS 1.3.21 branch released 2017-08-10
 
 Security
    * Fix authentication bypass in SSL/TLS: when authmode is set to optional,