[FIX] playground: fix name of playground component

docs/playground/playground.js

@@ -395,7 +395,7 @@ async function start() {
     loadFile("templates.xml"),
     whenReady()
   ]);
-  const rootApp = new App(App, { name: "Owl Playground" });
+  const rootApp = new App(Playground, { name: "Owl Playground" });
   rootApp.addTemplates(templates);
 
   await  rootApp.mount(document.body);

docs/playground/templates.xml

@@ -10,7 +10,7 @@
     <div class="code-editor" t-ref="editor"></div>
   </div>
 
-  <div t-name="Root" class="playground">
+  <div t-name="Playground" class="playground">
       <div class="left-bar" t-att-class="{split: state.splitLayout}"
            t-att-style="leftPaneStyle">
         <div class="menubar">