update changelog

Author: Jef Spaleta

CHANGELOG.md

@@ -6,6 +6,7 @@ This CHANGELOG follows the format listed [here](https://github.com/sensu-plugins
 ## [Unreleased]
 ### Changes
 - Updated development dependency to bundler ~> 2.1
+- Updated development dependency to rake ~> 13.0 
 - Updated runtime dependency to 'pg' '1.2.1' from 1.1   
 - Updated runtime dependency 'dentaku' '3.3.4' from 2.04