docs: fix readme of @vue/cli-plugin-eslint

[noi]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Underlying tools
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

Other information:

The default target directories of vue-cli-service lint command was written as src and test, but I think that src and tests are correct. If my opinion is correct, please merge.

Related code here:

vue-cli/packages/@vue/cli-plugin-eslint/lint.js

Lines 47 to 61 in 0380f22

	config.ignorePattern = [
	'!.*.js',
	'!{src,tests}/**/.*.js'
	]
	}
	const engine = new CLIEngine(config)
	const defaultFilesToLint = [
	'src',
	'tests',
	// root config files
	'*.js',
	'.*.js'
	]

[noi]

The checks passed, but github returns an error and remains pending. Can anyone please confirm it?

[haoqunjiang]

Thanks for spotting this!