message: upodate changelog with file extension
diff: ## Upcoming
  - `apollo`
  - - <First `apollo` related entry goes here>
  + - Add tsFileExtension flag to allow custom file extension in ts (like d.ts) [#1130](https://github.com/apollographql/apollo-tooling/pull/1130)
  - `apollo-codegen-core`
  - - <First `apollo-codegen-core` related entry goes here>
  + - Add tsFileExtension option to allow custom file extension in ts (like d.ts) [#1130](https://github.com/apollographql/apollo-tooling/pull/1130)
  - `apollo-codegen-flow`
  - <First `apollo-codegen-flow` related entry goes here>
  - `apollo-codegen-scala`
  - `apollo-codegen-swift`
  - <First `apollo-codegen-swift` related entry goes here>
  - `apollo-codegen-typescript`
  - - <First `apollo-codegen-typescript` related entry goes here>
  + - Add tsFileExtension option to allow custom file extension in ts (like d.ts) [#1130](https://github.com/apollographql/apollo-tooling/pull/1130)
  - `apollo-env`
  - <First `apollo-env` related entry goes here>
  - `apollo-graphql`
  