random_messages: update default interval

mods/random_messages/init.lua

@@ -27,7 +27,7 @@ function table.random( t )
 end
 
 function random_messages.initialize() --Set the interval in minetest.conf.
-	minetest.setting_set("random_messages_interval",1800)
+	minetest.setting_set("random_messages_interval",7200)
 	minetest.setting_save();
 	return 1800
 end