mine fix dor delayed closing time

src/engine/workthreads/MineThread.java

@@ -58,7 +58,7 @@ public class MineThread  implements Runnable {
                             mineWindowClose(mine); //mine was knocked down and was claimed, close window
                     }
                 }
-                nextPulse = LocalDateTime.now().plusMinutes(30);
+                nextPulse = nextPulse.plusMinutes(30);
             }
         }
     }