update eslint-webpack-plugin@2.4.1 and enable treads in linter

[marvelsrp]

I have perfomance problem in build. Results diff react-scripts@4.0.1 and react-scripts@3.4.3 in my project:

Default:

• react-scripts@3.4.3 eslint-loader@3.0.3, cache: true Done in 190.03s.
• react-scripts@4.0.1 eslint-webpack-plugin@2.4.1, cache: true Done in 369.82s.

Disable cache:

• react-scripts@3.4.3 eslint-loader@3.0.3, cache: false Done in 101.78s.
• react-scripts@4.0.1 eslint-webpack-plugin@2.4.1, cache: false Done in 101.98s.

Enable Treads:

• react-scripts@4.0.1 eslint-webpack-plugin@2.4.1, cache: true, treads: true Done in 106.12s.
• react-scripts@4.0.1 eslint-webpack-plugin@2.4.1, cache: false, treads: true Done in 84.70s.

I see performance improvement after package update eslint-webpack-plugin to 2.4.1 and enable multi treads linter.

Enable treads

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