removes deprecated yarn check in bin/setup

[adrienpoly]

Motivation / Background

While running a fresh Rails install I got a bunch of warnings from the command yarn check --check-files and dig a bit into the documentation

This Pull Request has been created because it appears the check command is deprecated and will be removed in Yarn 2.0

Detail

This Pull Request changes the generator to replace

system("yarn check --check-files") || system!("yarn install") 

by the recommended command

system("yarn install--check-files")

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[zzak]

I don't even think we've tried upgrading to Yarn 2, we're even using 1.x on CI afaik.

I've heard ideas floating around of us dropping yarn all together and use npm in places that still use node, that might be a concern of jsbundling; that is to say I'm not sure but if there are other places that are not Yarn 2.0 compatible they might be investigated.

Noticed that debian testing/unstable provide Yarn Modern, so that's an interesting data point to consider.

[adrienpoly]

Thanks for your review, here is a bit more information about why I came to investigate this.

• Clone a Rails project with a package.json
• run bin/setup

notice the 6 red error lines. This gave me a little WTF moment and I thought my setup went wrong. Those errors are the output of the current yarn check --check-files.

Another way to reproduce it is to run those commands in a project

rm -rf node_modules
bin/setup

This is the output with my proposed change

I think this change is beneficial as it drops a deprecated command from Yarn and it removes miss leading messages from bin/setup