Update changelog

Author: Abderrahmane Boudi

CHANGELOG.md

@@ -36,6 +36,11 @@ Fixes:
 
 ### master (unreleased)
 
+Features:
+
+- [#153](https://github.com/graphiti-api/graphiti/pull/153) Add after_graph_persist hook.
+  This hook fires after the graph of resources is persisted and before validation. (@A-Boudi)
+
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