update CHANGELOG

CHANGELOG.md

@@ -17,6 +17,7 @@ IMPROVEMENTS:
       protect against accidents. [GH-1595]
   * provider/aws: `aws_instance` supports placement groups [GH-1358]
   * provider/aws: `aws_elb` supports in-place changing of listeners [GH-1619]
+  * provider/aws: `aws_route53_record` supports weighted sets [GH-1578]
   * provider/docker: `docker_container` can specify links [GH-1564]
   * provider/openstack: Floating IP support for LBaaS [GH-1550]