Modify players before other plugins access them

Closes #123

plugin/src/main/java/com/lishid/openinv/listeners/PlayerListener.java

@@ -37,7 +37,7 @@ public class PlayerListener implements Listener {
         this.plugin = plugin;
     }
 
-    @EventHandler(priority = EventPriority.MONITOR)
+    @EventHandler(priority = EventPriority.LOWEST)
     public void onPlayerJoin(final PlayerJoinEvent event) {
         plugin.setPlayerOnline(event.getPlayer());
     }