fix ping

src/main/java/com/github/netricecake/kakao/TalkClient.java

@@ -34,7 +34,6 @@ import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-import java.util.concurrent.Future;
 
 public class TalkClient {
 
@@ -151,7 +150,7 @@ public class TalkClient {
             } catch (Exception e) {
                 e.printStackTrace();
             }
-        });
+        }).start();
     }
 
     public boolean sendMessage(long chatId, int type, String message, String extra) {