remove readonly of AuthenticationConnection in Session

Author: wizicer

src/Renci.SshNet/Session.cs

@@ -85,7 +85,7 @@ public class Session : ISession
         /// <remarks>
         /// Some server may restrict number to prevent authentication attacks
         /// </remarks>
-        private static readonly SemaphoreLight AuthenticationConnection = new SemaphoreLight(3);
+        private static SemaphoreLight AuthenticationConnection = new SemaphoreLight(3);
 
         /// <summary>
         /// Holds metada about session messages