Update v4-doc.md

Edward Xiao · web-flow · commit 28a766448535 · 2019-12-11T10:25:09.000+08:00
diff --git a/docs/v4-doc.md b/docs/v4-doc.md
@@ -764,7 +764,7 @@ Then in the component...
 
 ```js
 <Textbox
-  tabIndex="1" //Optional.[String or Number].Default: none.
+  attributesInput={{tabIndex: "1"}}
   ...
   validationOption={{
     ...
