update changelog for new iOS delegate method

Author: incanus

CHANGELOG.md

@@ -7,6 +7,7 @@
 - A new `MGLAnnotationImage.enabled` property allows you to disable touch events on individual annotations. ([#2501](https://github.com/mapbox/mapbox-gl-native/pull/2501))
 - Fixed a rendering issue that caused one-way arrows along tile boundaries to point due east instead of in the direction of travel. ([#2530](https://github.com/mapbox/mapbox-gl-native/pull/2530))
 - Fixed a rendering issue with styles that use the `background-pattern` property. ([#2531](https://github.com/mapbox/mapbox-gl-native/pull/2531))
+- A new delegate callback was added for observing taps to annotation callout views. ([#2596](https://github.com/mapbox/mapbox-gl-native/pull/2596))
 
 ## iOS 2.1.2