[tools] use ESLint class instead of CLIEngine

[tyankatsu0105]

Since version 7.0.0, ESLint supports ESLint class instead of CLIEngine class.
eslint/eslint#12939
eslint/rfcs#40

So, if it's possible, let's use ESLint class!

[ota-meshi]

Thank you for your suggestions!

But we will still support ESLint v6. So we may not need to replace it now.

However, I think it is possible to replace the CLIEngine of scripts that are not related to test cases at now.

[tyankatsu0105]

@ota-meshi
Oh sorry.
I overlooked supports version.
Umm...
Can I replace around tools?

[ota-meshi]

Can I replace around tools?

Yes. I think we can replace it.

[tyankatsu0105]

Great! Thanks for checking.
I will send PR😉