util.promisify doesn't exist on node v6

Author: zenbrent

package.json

@@ -25,6 +25,7 @@
     "standard": "^10.0.0",
     "standard-version": "^4.0.0",
     "sugarss": "^1.0.0",
+    "util.promisify": "^1.0.0",
     "webpack": "^3.0.0"
   },
   "scripts": {

test/helpers/fileChange.js

@@ -1,6 +1,6 @@
 const path = require('path')
 const { readFile, writeFile, unlink } = require('fs')
-const { promisify } = require('util')
+const promisify = require('util.promisify')
 
 const rf = promisify(readFile)
 const wf = promisify(writeFile)