fix(rxbindings) Make ConnectionStateEvent public (#774)

* fix(rxbindings) Make ConnectionStateEvent public

* Make class final

Author: rjuliano

rxbindings/src/main/java/com/amplifyframework/rx/RxOperations.java

@@ -102,7 +102,7 @@ public enum ConnectionState {
         /**
          * Describes events emitted by the {@link RxSubscriptionOperation} class.
          */
-        static class ConnectionStateEvent {
+        public static final class ConnectionStateEvent {
             private ConnectionState connectionState;
             private String subscriptionId;