Update Dgplug's Matrix room address

'#dgplug' IRC channel now online at irc.libera.chat[1].

[1]: https://dgplug.org/#contact

js/locations.js

@@ -47,7 +47,7 @@ var locations = [{
   "TITLE": "dgplug (Linux Users' Group of Durgapur)",
   "URL": "https://www.dgplug.org/",
   "MLIST": "http://lists.dgplug.org/listinfo.cgi/users-dgplug.org",
-  "MATURL": "https://matrix.to/#/#freenode_#dgplug:matrix.org",
+  "MATURL": "https://matrix.to/#/#dgplug:libera.chat",
   "TGURL": ""
 }, {
   "LAT": "18.975",