Add missing changelog entry (#819)

* Add missing changelog entry

* Update CHANGELOG.md

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Unreleased
 
+* [#818](https://github.com/Shopify/shopify_api/pull/818) Avoid depending on ActiveSupport
+
 * Freeze all string literals. This should have no impact unless your application is modifying ('monkeypatching') the internals of the library in an unusual way.
 
 * [#802](https://github.com/Shopify/shopify_api/pull/802) Made `inventory_quantity` a read-only field in Variant