Update index.js

Fix to .limit(n): if the next page is not a url (e.g. the link is broken or we reached the last page), the method should return fn(null, pages), and not call fn(null, pages) and continue to the next page.

index.js

@@ -138,7 +138,7 @@ function Xray() {
           if (!isUrl(url)) {
             debug('%j is not a url, finishing up', url);
             stream(obj, true);
-            fn(null, pages);
+            return fn(null, pages);
           }
 
           stream(obj);