update CHANGELOG

CHANGELOG.md

@@ -4,6 +4,8 @@ BUG FIXES:
 
   * core: math on arbitrary variables works if first operand isn't a
       numeric primitive. [GH-1381]
+  * core: avoid unnecessary cycles by pruning tainted destroys from
+      graph if there are no tainted resources [GH-1475]
   * command: remote states with uppercase types work [GH-1356]
   * provider/aws: launch configuration ID set after create success [GH-1518]
   * provider/openstack: region config is not required [GH-1441]