apollo: add changelog for schemaDiff removal

Author: evans

CHANGELOG.md

@@ -4,6 +4,9 @@
 - `apollo-codegen-scala`
   - Generate additional case-class like APIs for data containers [#943](https://github.com/apollographql/apollo-tooling/pull/943)
 
+- `apollo`
+  - remove schemaDiff and change types from code/exports [#967](https://github.com/apollographql/apollo-tooling/pull/967)
+
 ## `apollo@2.4.3`
 
 - `apollo-env@0.3.1`