update referenceCount log

[haiyang1985]

• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.7.3
• Operating System version: MacOs
• Java version: 1.8

Steps to reproduce this issue

This is not the issue, but the update of referenceCount log.

Originally, i don't know why we have to check the referenceCount before close the connection.

final class ReferenceCountExchangeClient implements ExchangeClient {
	@Override
	public void close(int timeout) {
	    if (referenceCount.decrementAndGet() <= 0) {
	        if (timeout == 0) {
	            client.close();

	        } else {
	            client.close(timeout);
	        }

	        replaceWithLazyClient();
	    }
	}
}