Refactor code-style

Author: wooorm

package.json

@@ -64,11 +64,7 @@
     "trailingComma": "none"
   },
   "xo": {
-    "prettier": true,
-    "rules": {
-      "no-var": "off",
-      "prefer-arrow-callback": "off"
-    }
+    "prettier": true
   },
   "remarkConfig": {
     "plugins": [

test.js

@@ -1,7 +1,7 @@
 import test from 'tape'
 import {heading} from './index.js'
 
-test('heading', function (t) {
+test('heading', (t) => {
   t.equal(heading(), false, 'should return `false` without node')
 
   t.equal(heading(null), false, 'should return `false` with `null`')