docs: fixed link to react-native-babel-transformer

[chronoB]

Summary

The link was pointing to the old metro-react-native-babel-transformer (changed in https://github.com/facebook/metro/pull/1024 to be located in the react-native repo)

Test plan

Link was pointing to a 404 and is now pointing to the correct location in the react-native repo

[facebook-github-bot]

@robhogan has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@robhogan has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@robhogan merged this pull request in facebook/metro@a941ba443881785b7f815c6df1c03bf669204967.