Eliminate wildcard import in mainline code.

Author: Steve Powell

src/com/rabbitmq/client/impl/HeartbeatSender.java

@@ -26,7 +26,7 @@
 import java.util.concurrent.ScheduledFuture;
 import java.io.IOException;
 
-import static java.util.concurrent.TimeUnit.*;
+import static java.util.concurrent.TimeUnit.SECONDS;
 
 /**
  * Manages heartbeat sending for a {@link AMQConnection}.