message: Add TypeScript def check to merge checklist
diff: @@ -9,6 +9,7 @@ Description of changes
  #### Merge checklist
  - [ ] Changed base branch to release branch
  +- [ ] Add or update TypeScript definitions (`index.d.ts`) if necessary
  - [ ] Tested in Chrome
  - [ ] Tested in Firefox
  - [ ] Tested in Safari
  