refactor [cdnjs] integration (#1668)

* pass error object to InvaildResponse()

this prevents us from throwing
TypeError: Cannot read property 'stack' of undefined
when we attempt to parse invalid json

* refactor [cdnjs] integration

lib/error-helper.js

@@ -39,7 +39,7 @@ async function asJson({ buffer, res }) {
   try {
     return JSON.parse(buffer);
   } catch (err) {
-    throw new InvalidResponse();
+    throw new InvalidResponse(undefined, err);
   }
 };