'no-unused-vars' shows varsIgnorePattern when argsIgnorePattern is not specified

[akouryy]

'no-unused-vars' shows varsIgnorePattern when argsIgnorePattern is not specified.

Tell us about your environment

• ESLint Version:
  4.13.1 and 4.14.0
• Node Version:
  8.1.3
• npm Version:
  5.6.0

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

Please show your full configuration:

Configuration

env:
  browser: true
  es6: true
extends: 'eslint:recommended'
parserOptions:
  sourceType: module
rules:
  eqeqeq: error
  indent:
    - error
    - 4
  linebreak-style:
    - error
    - unix
  quotes:
    - off
    - double
  semi:
    - error
    - always
  no-unused-vars:
    - error
    - varsIgnorePattern: "^_$"

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

/*
  no-unused-vars:
    - error
    - varsIgnorePattern: "^_$"
*/
buttonActions($('#next-word'), _ => changeWord(1), _ => changeWord(10));

$ eslint *.js

What did you expect to happen?
I expected it to report that argsIgnorePattern is not specified, which caused this error.

What actually happened? Please include the actual, raw output from ESLint.
It told me about varsIgnorePattern, which confused me and made it difficult to understand the problem.

error  '_' is defined but never used. Allowed unused vars must match /^_$/

[platinumazure]

Confirmed in the demo.

[akouryy]

I'm going to work on this.