Tell us about your environment

• ESLint Version: 6.1.0
• Node Version: 10.16.0
• npm Version: 6.9.0

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

default

Please show your full configuration:

```js
module.exports = {
  parserOptions: {
    ecmaVersion: 2015,
  },
};

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

/*eslint no-octal-escape: "error"*/

"\08"
"\09"

eslint index.js

What did you expect to happen?

2 errors

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

No errors

Are you willing to submit a pull request to fix this bug?

Yes, I'll be glad to do it. (#12079 should be merged first as this would collide)

Engines/parsers are already reporting these as octal escapes in strict mode:

"use strict";
"\08"

• Chrome: Octal escape sequences are not allowed in strict mode.
• Firefox: "0"-prefixed octal literals and octal escape sequences are deprecated; for octal literals use the "0o" prefix instead
• Espree: Octal literal in strict mode

Per the spec. 08 is not a valid escape sequence but it seems that it can be interpreted like 0 as a LegacyOctalEscapeSequence followed by a character 8.

LegacyOctalEscapeSequence::

OctalDigit[lookahead ∉ OctalDigit]

So I guess to be technically correct the rule should report \0?