Dispose queue in managed client.

Source/MQTTnet/Internal/BlockingQueue.cs

@@ -4,7 +4,7 @@ using System.Threading;
 
 namespace MQTTnet.Internal
 {
-    public class BlockingQueue<TItem>
+    public class BlockingQueue<TItem> : IDisposable
     {
         private readonly object _syncRoot = new object();
         private readonly LinkedList<TItem> _items = new LinkedList<TItem>();
@@ -108,5 +108,10 @@ namespace MQTTnet.Internal
                 _items.Clear();
             }
         }
+
+        public void Dispose()
+        {
+            _gate.Dispose();
+        }
     }
 }