Bug 1830265 - Enable ESLint and Prettier on .babel-eslint.rc.js. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D176637

.babel-eslint.rc.js

@@ -2,8 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+/* eslint-env node */
+
 module.exports = {
-  plugins: [
-    "@babel/plugin-syntax-jsx",
-  ],
+  plugins: ["@babel/plugin-syntax-jsx"],
 };

.eslintignore

@@ -9,6 +9,7 @@
 
 !.eslintrc*.js
 !.prettierrc.js
+!.babel-eslint.rc.js
 
 # Always ignore node_modules.
 **/node_modules/