Switch to Mastodon as Twitter link still broken

Author: geographika

doc/contact.rst

@@ -32,7 +32,7 @@ assistance. You also can meet us at Slack, Matrix or Gitter.
 A wealth of information is available on our `Wiki site <https://trac.osgeo.org/osgeolive/wiki>`_, 
 and a `bug and wish tracking system <https://trac.osgeo.org/osgeolive/report/10>`_ is also available.
 
-Stay tuned and follow OSGeoLive on Twitter `@osgeolive <https://twitter.com/osgeolive>`_.
+Stay tuned and follow OSGeoLive on Mastodon `@osgeolive <https://fosstodon.org/@osgeolive>`_.
 
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