Upgrade mina-core to 2.0.21 (#2)

diff --git a/pom.xml b/pom.xml
index 878daba..f87ee2d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -108,7 +108,7 @@
       <dependency>
         <groupId>org.apache.mina</groupId>
         <artifactId>mina-core</artifactId>
-        <version>2.0.4</version>
+        <version>2.0.21</version>
       </dependency>
 
       <dependency>
diff --git a/server/core/src/main/java/org/apache/vysper/mina/XmppIoHandlerAdapter.java b/server/core/src/main/java/org/apache/vysper/mina/XmppIoHandlerAdapter.java
index 6332033..3d07c3b 100644
--- a/server/core/src/main/java/org/apache/vysper/mina/XmppIoHandlerAdapter.java
+++ b/server/core/src/main/java/org/apache/vysper/mina/XmppIoHandlerAdapter.java
@@ -104,6 +104,11 @@
         // TODO implement
     }
 
+    @Override
+    public void inputClosed(IoSession ioSession) throws Exception {
+        ioSession.closeNow();
+    }
+
     public void sessionCreated(IoSession ioSession) throws Exception {
         SessionStateHolder stateHolder = new SessionStateHolder();
         SessionContext sessionContext = new MinaBackedSessionContext(serverRuntimeContext, stateHolder, ioSession);