Update sandbox title

Author: egaga

sandbox.html

@@ -6,7 +6,7 @@
   <link rel="stylesheet" type="text/css" href="css/css.css?version={VERSION}" />
   <link rel="icon" type="image/png" href="icon.png"/>
 
-  <title>Interactive Vim tutorial - sandbox</title>
+  <title>OpenVim - Interactive Vim tutorial - Sandbox</title>
 
   <!-- GENERAL (mostly) -->
   <!--