ensure to use "engines.npm" 4.6.1

package.json

@@ -136,7 +136,7 @@
   },
   "engines": {
     "node": "6.11.3",
-    "npm": "5.4.2",
+    "npm": "4.6.1",
     "yarn": "1.1.0"
   },
   "config": {