home: add slack link redirect

Author: bryanvu

_layouts/home.html

@@ -37,7 +37,7 @@ <h2>Community</h2>
     to keep posted about LND.
   </p>
   <p>Join the 
-    <a href="https://join.slack.com/t/lightningcommunity/shared_invite/enQtMzQ0OTQyNjE5NjU1LThmOGJkZDIzY2U2ODI5ODhmOWMzM2FkOTY5ZTdkYTc5NDYyN2U1YTJkZTE1MWU2OTZlZTAyOWY4NGY2M2M1NTM">LND Developer Slack</a>
+    <a href="https://lightning.engineering/slack.html">LND Developer Slack</a>
     to meet the team, discuss development, and hang out!
   </p>
   </section>