chore(package): update pify to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -55,7 +55,7 @@
     "mocha": "^5.0.0",
     "nodecat": "^2.0.0",
     "nyc": "^12.0.2",
-    "pify": "^3.0.0",
+    "pify": "^4.0.0",
     "rimraf": "^2.2.0"
   },
   "engines": {