go.dev/_content/js: upgrade fallback version to go1.17 in site.js

We can start using Go 1.17, the most recent release, as the fallback.

Change-Id: I05685c99852cc34c79706a2f8916c6dc29849062
Reviewed-on: https://go-review.googlesource.com/c/website/+/345829
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/go.dev/_content/js/site.js b/go.dev/_content/js/site.js
index 23e4480..ca99b6b 100644
--- a/go.dev/_content/js/site.js
+++ b/go.dev/_content/js/site.js
@@ -157,7 +157,7 @@
    * Retrieves list of Go versions & returns the latest
    */
   async function getLatestVersion() {
-    let version = 'go1.15'; // fallback version if fetch fails
+    let version = 'go1.17'; // fallback version if fetch fails
     try {
       const versionData = await (
         await fetch('https://golang.org/dl/?mode=json')