[release] src/welcome: correct link to Gophers Slack

The link should be an invite, since people without accounts won't be
able to see the channel.

Change-Id: If3554e4cd7b8ee694e06ff650101a5c003d20761
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/286892
Trust: Rebecca Stambler <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
(cherry picked from commit 63d2287)
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/286913

Author: stamblerre

src/welcome.ts

@@ -159,7 +159,7 @@ setting, we recommend removing that setting now.`;
 						-->
 						<li><a href="#" class="Command" data-command="openDocument" data-document="CHANGELOG.md">Release notes</a></li>
 						<li><a href="https://github.com/golang/vscode-go">GitHub</a></li>
-						<li><a href="https://gophers.slack.com/messages/vscode/">Slack</a></li>
+						<li><a href="https://invite.slack.golangbridge.org/">Slack</a></li>
 					</ul>
 				</div>
 			</div>