message: Fix typo in Contributing document
diff: @@ -65,7 +65,7 @@ Tips for a faster workflow:
  - Run `npm start` in one terminal. This watches the source tree and compiles it incrementally.
  - When desired, run `npm run unit-test` in another terminal. This runs tests using the compilation output from `npm start`.
  -- Run `npm run unit-test:deubg` to use headful DevTools to debug or develop tests
  +- Run `npm run unit-test:debug` to use headful DevTools to debug or develop tests
  - For testing specific a package, use `--package` flag, e.g., `npm run unit-test -- --package=@pixi/math`
  - The `--package` flag supports multiple packages, e.g., `npm run unit-test -- --package=@pixi/math --package=@pixi/core`
  - The `--package` flag supports debug testing as well, e.g., `npm run unit-test:debug -- --package=@pixi/math`
  