some fix and update document

src/utils.js

@@ -268,24 +268,24 @@ function showError(show, text) {
   }
 }
 
-function showSuccess(show, text) {
+function showSuccess(show, text, time = 3000) {
   if (show) {
-    buildNotification('success', text);
+    buildNotification('success', text, time);
     notificationEl.open();
   } else {
     notificationEl && notificationEl.close();
   }
 }
 
-function buildNotification(type, text) {
+function buildNotification(type, text, duration = -1) {
+  const param = {
+    type,
+    text,
+    duration
+  }
   if (!notificationEl) {
-    notificationEl = new Kuc.Notification({
-      type,
-      text
-    });
+    notificationEl = new Kuc.Notification(param);
   } else {
-    notificationEl.close();
-    notificationEl.type = type;
-    notificationEl.text = text;
+    Object.assign(notificationEl, param)
   }
 }