Fix typo in a11y for yarn

Author: dandv

packages/eslint-config-airbnb/README.md

@@ -12,7 +12,7 @@ We export three ESLint configurations for your usage.
 
 Our default export contains all of our ESLint rules, including ECMAScript 6+ and React. It requires `eslint`, `eslint-plugin-import`, `eslint-plugin-react`, and `eslint-plugin-jsx-a11y`. If you don't need React, see [eslint-config-airbnb-base](https://npmjs.com/eslint-config-airbnb-base).
 
-If you use yarn, run `yarn add --dev eslint-config-airbnb-base eslint-plugin-import eslint-plugin-react eslint-plugin-jsx-a11`, and see below for npm instructions.
+If you use yarn, run `yarn add --dev eslint-config-airbnb-base eslint-plugin-import eslint-plugin-react eslint-plugin-jsx-a11y`, and see below for npm instructions.
 
 1. Install the correct versions of each package, which are listed by the command: