Updated IRC channel info to libera.chat.

The IRC channel moved networks to libera.chat. See you there! :)

.travis.yml

@@ -13,5 +13,5 @@ addons:
 notifications:
   irc:
     channels:
-      - "chat.freenode.net#libopencm3"
+      - "irc.libera.chat#libopencm3"
     use_notice: true

README.md

@@ -191,7 +191,7 @@ Community
 ---------
 
  * Our [![Gitter channel](https://badges.gitter.im/libopencm3/discuss.svg)](https://gitter.im/libopencm3/discuss)
- * Our IRC channel on the freenode IRC network is called #libopencm3
+ * Our IRC channel on the libera.chat IRC network is called #libopencm3
 
 Mailing lists
 -------------