update /th/tour/traits page

Author: fResult

_th/tour/traits.md

@@ -152,6 +152,10 @@ iterator.next()  // returns 1
 
 {% tab 'Scala 2' for=trait-pet-example %}
 
+{% tabs trait-pet-example class=tabs-scala-version %}
+
+{% tab 'Scala 2' for=trait-pet-example %}
+
 ```scala mdoc
 import scala.collection.mutable.ArrayBuffer