Update demo website to use 3.4.0

index.html

@@ -96,7 +96,7 @@
         // In development we import locally.
         window.location.hostname === "localhost"
           ? "/dist/web/install-button.js"
-          : "https://unpkg.com/esp-web-tools@3.3.0/dist/web/install-button.js?module"
+          : "https://unpkg.com/esp-web-tools@3.4.0/dist/web/install-button.js?module"
       );
     </script>
   </head>
@@ -192,7 +192,7 @@
       <pre>
 &lt;script
   type="module"
-  src="https://unpkg.com/esp-web-tools@3.3.0/dist/web/install-button.js?module"
+  src="https://unpkg.com/esp-web-tools@3.4.0/dist/web/install-button.js?module"
 >&lt;/script>
 
 &lt;esp-web-install-button