fix ie8 forEach

@@ -4,11 +4,11 @@ var cdnDomains = require('../../../../config/dns-prefetch');
 
 function cdnReplace(cdn, imgUrl) {
     if (cdn === 'qcloud') {
-        Object.keys(cdnDomains).forEach(key => {
+        for (var key in cdnDomains) {
             if (imgUrl.indexOf(key) >= 0) {
                 imgUrl = imgUrl.replace(key, cdnDomains[key]);
             }
-        });
+        }
     }
     return imgUrl;
 }