nit

Author: slandelle

extras/rxjava/src/main/java/org/asynchttpclient/extras/rxjava/UnsubscribedException.java

@@ -15,6 +15,7 @@
 /**
  * Indicates that an {@code Observer} unsubscribed during the processing of a HTTP request.
  */
+@SuppressWarnings("serial")
 public class UnsubscribedException extends RuntimeException {
 
     public UnsubscribedException() {