send feedback if isArray is not supported

www/common/cryptpad-common.js

@@ -1189,6 +1189,11 @@ define([
             if (typeof(window.Proxy) === 'undefined') {
                 feedback("NO_PROXIES");
             }
+
+            if (typeof(Array.isArray) === 'function') {
+                feedback("NO_ISARRAY");
+            }
+
             $(function() {
                 // Race condition : if document.body is undefined when alertify.js is loaded, Alertify
                 // won't work. We have to reset it now to make sure it uses a correct "body"