fix multiple subscribing only received one message bug.

src/DotNetCore.CAP.Kafka/KafkaConsumerClient.cs

 using System;
+using System.Collections.Generic;
 using System.Text;
 using System.Threading;
 using Confluent.Kafka;
@@ -25,19 +26,18 @@ namespace DotNetCore.CAP.Kafka
             StringDeserializer = new StringDeserializer(Encoding.UTF8);
         }
 
-        public void Subscribe(string topic)
+        public void Subscribe(IEnumerable<string> topics)
         {
-            Subscribe(topic, 0);
-        }
+            if (topics == null)
+                throw new ArgumentNullException(nameof(topics));
 
-        public void Subscribe(string topicName, int partition)
-        {
             if (_consumerClient == null)
             {
                 InitKafkaClient();
             }
-            _consumerClient.Assignment.Add(new TopicPartition(topicName, partition));
-            _consumerClient.Subscribe(topicName);
+
+            //_consumerClient.Assign(topics.Select(x=> new TopicPartition(x, 0)));
+            _consumerClient.Subscribe(topics);
         }
 
         public void Listening(TimeSpan timeout, CancellationToken cancellationToken)

src/DotNetCore.CAP/IConsumerClient.cs

 using System;
+using System.Collections.Generic;
 using System.Threading;
 
 namespace DotNetCore.CAP
@@ -8,9 +9,7 @@ namespace DotNetCore.CAP
     /// </summary>
     public interface IConsumerClient : IDisposable
     {
-        void Subscribe(string topic);
-
-        void Subscribe(string topic, int partition);
+        void Subscribe(IEnumerable<string> topics);
 
         void Listening(TimeSpan timeout, CancellationToken cancellationToken);
 

src/DotNetCore.CAP/IConsumerHandler.Default.cs

 using System;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DotNetCore.CAP.Infrastructure;
@@ -56,10 +57,7 @@ namespace DotNetCore.CAP
                     {
                         RegisterMessageProcessor(client);
 
-                        foreach (var item in matchGroup.Value)
-                        {
-                            client.Subscribe(item.Attribute.Name);
-                        }
+                        client.Subscribe(matchGroup.Value.Select(x => x.Attribute.Name));
 
                         client.Listening(_pollingDelay, _cts.Token);
                     }