Fix changelog for ssl_server2.c usage fix
diff --git a/ChangeLog b/ChangeLog
index 2bd0be9..42cbf6c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,7 @@
 Bugfix
    * Fix memory leak in mbedtls_ssl_set_hostname() when called multiple times.
      Found by projectgus and jethrogb, #836.
+   * Fix usage help in ssl_server2 example. Found and fixed by Bei Lin.
 
 = mbed TLS 2.1.9 branch released 2017-08-10