Add missing headings to changelog

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 [diff](https://github.com/prettier/prettier/compare/1.19.0...1.19.1)
 
+### CLI
+
 #### Fix `--stdin` regression in 1.19.0 ([#6894](https://github.com/prettier/prettier/pull/6894) by [@lydell](https://github.com/lydell))
 
 <!-- prettier-ignore -->
@@ -15,6 +17,8 @@ $ echo "test" | prettier --stdin --parser babel
 test;
 ```
 
+### TypeScript
+
 #### Fix formatting of union type as arrow function return type ([#6896](https://github.com/prettier/prettier/pull/6896) by [@thorn0](https://github.com/thorn0))
 
 <!-- prettier-ignore -->