upgrade engines section of package.json

package.json

@@ -218,7 +218,7 @@
   },
   "engines": {
     "node": ">=8.11.1 <9",
-    "npm": ">=5.6.0 <6",
+    "npm": ">=5.6.0 <7",
     "yarn": "^1.5.1"
   },
   "config": {