#354 | Add missing import

Author: slayful

src/test/java/com/rabbitmq/client/test/functional/Metrics.java

@@ -22,6 +22,7 @@
 import com.rabbitmq.client.DefaultConsumer;
 import com.rabbitmq.client.Envelope;
 import com.rabbitmq.client.GetResponse;
+import com.rabbitmq.client.MessageProperties;
 import com.rabbitmq.client.Recoverable;
 import com.rabbitmq.client.RecoveryListener;
 import com.rabbitmq.client.impl.StandardMetricsCollector;