Update Tabs.md

The function name and argument were wrong, probably remains of some old version. 
If you update this code also on the CodePen project, it will print to the console, like intended

snippets/Tabs.md

@@ -45,7 +45,7 @@ const TabItem = props => <div {...props} />;
 const Tabs = ({ defaultIndex = 0, onTabClick, children }) => {
   const [bindIndex, setBindIndex] = React.useState(defaultIndex);
   const changeTab = newIndex => {
-    if (typeof onItemClick === 'function') onItemClick(itemIndex);
+    if (typeof onTabClick === 'function') onTabClick(newIndex);
     setBindIndex(newIndex);
   };
   const items = children.filter(item => item.type.name === 'TabItem');