Revert Slack *invite* link to HTTP

Whilst Slack itself is HTTPS, the invite link is HTTP. This reverts the change from July 2021 that broke the invite link by changing it to HTTPS.

Author: seancorfield

content/community/resources.adoc

@@ -45,7 +45,7 @@ View & more…)
 === Chat
 
 * IRC: `#clojurescript` on https://freenode.net/[freenode.net]
-* Slack: `#clojurescript` on https://clojurians.slack.com/[Clojurians Slack] (https://clojurians.net/[get an invite here])
+* Slack: `#clojurescript` on https://clojurians.slack.com/[Clojurians Slack] (http://clojurians.net/[get an invite here])
 ** searchable chat logs can be found https://clojurians.zulipchat.com/#narrow/stream/180378-slack-archive/topic/clojurescript[here], and https://clojurians-log.clojureverse.org/[here]
 * Zulip: `#clojurescript` on https://clojurians.zulipchat.com/#narrow/stream/151762-clojurescript[Clojurians Zulip Chat]