Use yarn instead of npm about gatsby-starter

[JanLenoch]

Is Yarn capable of properly merging edits of package-lock.json made in two simultaneously running git branches? If yes, I'd vote for that too. Otherwise I'm not sure if it helped in such situations.

[Simply007]

yarn is not using package-lock.json, it is using yarn.lock file.

it is necessary to remove package-lock.json and run yarn command to install dependencies and generate yarn.lock file.
And it is required to adjust the Readme.md file according to the setup.

It would be best to configure Netlify checks to run yearn as well to have all configuration consistent.

[Simply007]

Yarn was not implemented in referenced pull request - let's leave it opened.

[tom-raley]

Was this ever addressed? If not, I'd like to give it a go.