Configure ESLint using a JS file instead of JSON (#1868)

The file is meant to be written by humans.

Author: matthiask

.eslintrc.json renamed to .eslintrc.js

@@ -1,7 +1,9 @@
-{
+module.exports = {
+    root: true,
     "env": {
         "browser": true,
-        "es6": true
+        "es6": true,
+        node: true,
     },
     "extends": "eslint:recommended",
     "parserOptions": {
@@ -17,4 +19,4 @@
         "prefer-const": "error",
         "semi": "error"
     }
-}
+};