Fix documentation on default linted files

[Robin-Hoodie]

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 documentation mentions all files in the src and tests directories are linted by default. Upon inspection of the sourcecode however, it seems that also Javascript files in the root directory are being linted by default.

I stumbled upon this when trying to figure out why my .eslintrc.js file itself was being linted by running vue-cli-service lint without passing any args.

[fangbinwei]

.*.js like .eslintrc.js will be linted only if there is no .eslintignore in project according to

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

Line 39 in 3eaef4d

if (!fs.existsSync(api.resolve('.eslintignore')) && !config.ignorePattern) {

.Maybe it's not worth mentioning ?

If .eslintignore exists and we want to lint .eslintrc.js, !.*.js should be added to .eslintignore

[Robin-Hoodie]

I wasn't aware dot-files were not being linted by default by ESLint. I also wasn't aware that the default behaviour of vue-cli-service lint is to override that default behavior of ESLint.

Perhaps it's best to mention both behaviours then?

Something along the lines of:

vue-cli-service lint will by default lint hidden dot-files if there is no .eslintignore file or ignorePatterns property in your ESLint config. This behaviour is in contrast to ESLint's default behaviour, which will not lint dot-files by default. If you want to follow ESLint's default behaviour instead, consider adding an (empty) .eslintignore file or any ignorePatterns property to your ESLint config file

[fangbinwei]

We prefer not to describe the default behavior of ESlint, which may change. ESlint@7 no longer ignores .eslintrc.js,

:::tip
`vue-cli-service lint` will lint dotfiles `.*.js` by default. If you want to follow ESLint's default behavior instead, consider adding a `.eslintignore` file in your project.
:::

[fangbinwei]

Thanks a lot