Fix markdown in changelog

Author: LegNeato

juniper/CHANGELOG.md

@@ -4,7 +4,7 @@
 
 # [[0.15.4] 2021-04-03](https://github.com/graphql-rust/juniper/releases/tag/juniper-0.15.4)
 
-- Un-deprecate select_child, has_child, and child_names methods ([#900]https://github.com/graphql-rust/juniper/pull/#900)
+- Un-deprecate select_child, has_child, and child_names methods ([#900](https://github.com/graphql-rust/juniper/pull/#900))
 
 # [[0.15.3] 2021-01-27](https://github.com/graphql-rust/juniper/releases/tag/juniper-0.15.3)