update for 7.4.3 release

Author: jmckenna

HISTORY.TXT

@@ -12,6 +12,11 @@ For a complete change history, please see the Git log comments.  For more
 details about recent point releases, please see the online changelog at:
 http://mapserver.org/development/changelog/
 
+7.4.3 release (2019-12-16)
+--------------------------
+
+- No major changes, see detailed changelog for bug fixes
+
 7.4.2 release (2019-9-13)
 -------------------------