update package.json

package.json

@@ -135,9 +135,9 @@
     "sinon-chai": "^2.13.0"
   },
   "engines": {
-    "node": "6.11.3",
-    "npm": "4.6.1",
-    "yarn": "1.1.0"
+    "node": ">=6.11 <7",
+    "npm": ">=4.6 <5",
+    "yarn": "~1.1.0"
   },
   "config": {
     "blanket": {