change auth to interna_hashed

because why the fuck not?

roles/xmpp/templates/prosody.cfg.lua.j2

 -- server please see http://prosody.im/doc/modules/mod_auth_internal_hashed
 -- for information about using the hashed backend.
 
-authentication = "internal_plain"
+authentication = "internal_hashed"
 
 -- Select the storage backend to use. By default Prosody uses flat files
 -- in its configured data directory, but it also supports more backends