Fix slow recompile times for existing users

[fkirc]

#9886 was a crippling performance regression that rendered react-scripts close to unusable, at least for all my projects where I was using it.
Fortunately, this performance regression was fixed by the following release of eslint-webpack-plugin: https://github.com/webpack-contrib/eslint-webpack-plugin/releases/tag/v2.4.1 (otherwise I would have been forced to downgrade to react-scripts 3.X).

However, the performance regression was only fixed for new users of react-scripts, but not for existing users.
The problem is that the internal dependency to eslint-webpack-plugin still accepts broken versions it its admissible range of versions.
Therefore, existing users are forced to read through #9886 until they find out that they either have to manually bump eslint-webpack-plugin or delete their entire package-lock.json and re-install everything from scratch.

So this PR is an attempt to fix the performance regression for all users that are updating react-scripts, instead of waiting until they read through GitHub bug reports or delete their package-lock files.

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[marvelsrp]

Hello, I have same problem. Update to 2.4.1 don't fix. Need add treads: true flag for upgrade performance eslint.
#10249

[fkirc]

Hello, I have same problem. Update to 2.4.1 don't fix. Need add treads: true flag for upgrade performance eslint.
#10249

For me, updating the package-lock to 2.4.1 was sufficient.
But anyways, thank you for filing a second PR; this should increase the chances of getting it fixed.

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[Saibamen]

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