Update interface for install event in summary table (w3c#1706)

Following w3c#1701, the `install` event now uses the `InstallEvent` interface.

docs/index.bs

@@ -1833,7 +1833,7 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
       <tbody>
         <tr>
           <td><dfn event id="service-worker-global-scope-install-event"><code>install</code></dfn></td>
-          <td>{{ExtendableEvent}}</td>
+          <td>{{InstallEvent}}</td>
           <td>[=Lifecycle Event|Lifecycle=]</td>
           <td>The [=ServiceWorkerGlobalScope/service worker=]'s <a>containing service worker registration</a>'s <a>installing worker</a> changes. (See step 11.2 of the <a>Install</a> algorithm.)</td>
         </tr>