update CHANGELOG

Author: eheydrick

CHANGELOG.md

@@ -4,6 +4,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This CHANGELOG follows the format listed at [Keep A Changelog](http://keepachangelog.com/)
 
 ## [Unreleased]
+### Fixed
+- metrics-postgres-query.rb: Fix `count_tuples` option
 
 ## [1.0.0] - 2016-12-27
 ### Fixed