Restrict MD5 in x509 certificates

Remove support for X509 certificates signed with MD5.
Issue raised by Harm Verhagen
diff --git a/ChangeLog b/ChangeLog
index 5099081..cf2defa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.x.xx branch released xxxx-xx-xx
+
+Bugfix
+   * Remove support for X509 certificates signed with MD5.
+     Issue raised by Harm Verhagen
+
 = mbed TLS 1.3.19 branch released 2017-03-08
 
 Security