message: Fix minor possessive typo
diff: @@ -28,7 +28,7 @@ the code.
  sub-folder which is used for a markdown spellchecker.
  - [`.yarn/`](https://github.com/backstage/backstage/tree/master/.yarn) -
  - Backstage ships with it's own `yarn` implementation. This allows us to have
  + Backstage ships with its own `yarn` implementation. This allows us to have
  better control over our `yarn.lock` file and hopefully avoid problems due to
  yarn versioning differences.
  