update to be compatible with older dotnet version

concurrent/EzyEventLoopEvent.cs

@@ -4,8 +4,8 @@ public interface EzyEventLoopEvent
     {
         bool call();
 
-        void onFinished() { }
+        void onFinished();
 
-        void onRemoved() { }
+        void onRemoved();
     }
 }

concurrent/EzyEventLoopGroup.cs

@@ -345,6 +345,11 @@ public void onFinished()
             {
                 eventLoopByEvent.Remove(this);
             }
+
+            public void onRemoved()
+            {
+                // do nothing
+            }
         }
 
         public class ScheduledEvent : EzyEventLoopEvent

socket/EzyPingSchedule.cs

@@ -34,7 +34,17 @@ public bool call()
             return true;
         }
 
-		public virtual void start()
+        public void onFinished()
+        {
+            // do nothing
+        }
+
+        public void onRemoved()
+        {
+            // do nothing
+        }
+
+        public virtual void start()
 		{
             int periodMillis = pingManager.getPingPeriod();
             if (eventLoopGroup != null)

socket/EzySocketAdapter.cs

@@ -53,6 +53,11 @@ public void onFinished()
             setStopped(true);
         }
 
+        public void onRemoved()
+        {
+            // do nothing
+        }
+
         protected abstract String getThreadName();
 
         protected virtual void run()