Update CHANGELOG.md

CHANGELOG.md

@@ -49,6 +49,7 @@ IMPROVEMENTS:
       static default value [GH-1632]
   * provider/aws: automatically set the private IP as the SSH address
       if not specified and no public IP is available [GH-1623]
+  * provider/aws: `aws_elb` exports `source_security_group` field [GH-1708]
   * provider/docker: `docker_container` can specify links [GH-1564]
   * provider/google: `resource_compute_disk` supports snapshots [GH-1426]
   * provider/google: `resource_compute_instance` supports specifying the