_content/doc: update link to Gophers Discord

Changed to vanity URL after becoming a Discord Partnered server.

Change-Id: I8c59574697c8202b7fe1777478d3abe708d02301
GitHub-Last-Rev: 5f857b73e8bc32c879b6410829f7558d231ed82e
GitHub-Pull-Request: golang/website#45
Reviewed-on: https://go-review.googlesource.com/c/website/+/306049
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
diff --git a/_content/doc/help.html b/_content/doc/help.html
index 3d32ae5..ecfbbc6 100644
--- a/_content/doc/help.html
+++ b/_content/doc/help.html
@@ -27,7 +27,7 @@
 forum for Go programmers.
 </p>
 
-<h3 id="discord"><a href="https://discord.gg/64C346U">Gophers Discord</a></h3>
+<h3 id="discord"><a href="https://discord.gg/golang">Gophers Discord</a></h3>
 <p>
 Get live support and talk with other gophers on the Go Discord.
 </p>