update pkgcloud and use version 2.x

package.json

@@ -2,7 +2,7 @@
   "name": "loopback-component-storage",
   "description": "Loopback Storage Service",
   "engines": {
-    "node": ">=6"
+    "node": ">=8"
   },
   "version": "3.6.0",
   "main": "index.js",
@@ -15,7 +15,7 @@
     "async": "^2.6.1",
     "debug": "^3.1.0",
     "formidable": "^1.2.1",
-    "pkgcloud": "^1.5.0",
+    "pkgcloud": "^2.0.0",
     "strong-globalize": "^4.1.1",
     "uuid": "^3.2.1"
   },