Add a ChangeLog entry for memory leak in mbedtls_x509_csr_parse()

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index be0026e..e75f5e7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.x.x branch released xxxx-xx-xx
+
+Bugfix
+   * Fix a memory leak in mbedtls_x509_csr_parse(), found by catenacyber,
+     Philippe Antoine.
+
 = mbed TLS 2.7.4 branch released 2018-06-18
 
 Bugfix