Fix CORS proxy

Author: niutech

htmlpreview.js

@@ -89,10 +89,11 @@
 	var fetchProxy = function (url, options, i) {
 		var proxy = [
 			'https://cors-anywhere.herokuapp.com/',
-			'https://yacdn.org/serve/',
+			'https://yacdn.org/proxy/',
 			'https://api.codetabs.com/v1/proxy/?quest='
 		];
 		return fetch(proxy[i] + url, options).then(function (res) {
+			if (!res.ok) throw new Error('Cannot load ' + url + ': ' + res.status + ' ' + res.statusText);
 			return res.text();
 		}).catch(function (error) {
 			if (i === proxy.length - 1)