Update IRC/Matrix links

- libera instead of freenode
- element instead of riot

Author: ThiefMaster

_layouts/contact.html

@@ -23,8 +23,8 @@ <h1>Contact Us</h1>
                 <div class="row justify-content-center">
                     <div class="col-sm-4 col-12">
                         <h2 class="uppercase">IRC Channel</h2>
-                        <div>Official <a href="https://webchat.freenode.net/?channels=indico">#indico</a> channel at Freenode (<b>irc.freenode.net</b>)</div>
-                        <div>Also accessible through <a href="https://riot.im/app/#/room/#indico:matrix.org">Matrix</a>.</div>
+                        <div>Official <a href="https://web.libera.chat/gamja/?channels=#indico">#indico</a> channel at Libera.Chat (<b>irc.libera.chat</b>)</div>
+                        <div>Also accessible through <a href="https://app.element.io/#/room/#indico:matrix.org">Matrix</a>.</div>
                     </div>
                     <div class="col-sm-4 col-12">
                         <h2 class="uppercase">Discussion Forum</h2>