Update CHANGELOG.md

Author: LegNeato

juniper/CHANGELOG.md

@@ -1,6 +1,7 @@
 # master
 
-- No changes yet
+- Update GraphQL Playground to v1.7.27.
+- Add marker GraphQL trait implementations for Rust container types like `Box`([#847](https://github.com/graphql-rust/juniper/pull/847))
 
 # [[0.15.1] 2020-12-12](https://github.com/graphql-rust/juniper/releases/tag/juniper-0.15.1)