Fix inaccurate online player count for Discord leave message

Author: JRoy

EssentialsDiscord/src/main/java/net/essentialsx/discord/listeners/BukkitListener.java

@@ -139,7 +139,7 @@ public void sendJoinQuitMessage(final Player player, final String message, Messa
                         MessageUtil.sanitizeDiscordMarkdown(player.getName()),
                         MessageUtil.sanitizeDiscordMarkdown(player.getDisplayName()),
                         MessageUtil.sanitizeDiscordMarkdown(message),
-                        jda.getPlugin().getEss().getOnlinePlayers().size(),
+                        jda.getPlugin().getEss().getOnlinePlayers().size() - 1,
                         userCount),
                         player);
     }