What is the purpose of this pull request? (put an "X" next to item)

[X] Bug fix

This is a small fix that prevents dot-notation from converting bigint and some regex literals to null in Node 8.

Demo link - the error is observable if you open this link in Firefox (which also doesn't support the syntax, like Node 8).

Tell us about your environment

• ESLint Version: 6.1.0
• Node Version: 8.16.0
• npm Version: 6.4.1

What parser (default, Babel-ESLint, etc.) are you using?

default

Please show your full configuration:

module.exports = {
  parserOptions: {
    ecmaVersion: 2018,
  },
};

What did you do? Please include the actual source code causing the issue.

/*eslint dot-notation:error*/

a[/(?<zero>0)/];

What did you expect to happen?

No warnings.

What actually happened? Please include the actual, raw output from ESLint.

Warning and the fix:

/*eslint dot-notation:error*/

a.null;

What changes did you make? (Give an overview)

Fixed dot-notation to explicitly check only "string", "boolean" and null literals.

Is there anything you'd like reviewers to focus on?

The test in valid fails in Node 8 before the fix. Tests in invalid are for regression only.