fix(deps): update dependency npm to v6 [security]

Author: renovate[bot]

package.json

@@ -56,6 +56,6 @@
     "body-parser": "^1.15.2",
     "express": "^4.14.0",
     "install": "^0.8.2",
-    "npm": "^3.10.9"
+    "npm": "^6.14.6"
   }
 }