Replace 'Project Tango' with 'ARCore'

Remove reference to Project Tango and replace with ARCore

codelab-elements/google-codelab-index/index.html

@@ -58,7 +58,7 @@
         <h2>Welcome to Codelabs!</h2>
         <p>Google Developers Codelabs provide a guided, tutorial, hands-on coding experience. Most codelabs will step you through
           the process of building a small application, or adding a new feature to an existing application. They cover a wide
-          range of topics such as Android Wear, Google Compute Engine, Project Tango, and Google APIs on iOS.</p>
+          range of topics such as Android Wear, Google Compute Engine, ARCore, and Google APIs on iOS.</p>
       </div>
     </header>
     <main>