Fix compilation in simple transport test case base

This commit fixes compilation after a backport gone bad due to a
difference in the minimum Java version between 7.x and master.

test/framework/src/main/java/org/elasticsearch/transport/AbstractSimpleTransportTestCase.java

@@ -28,6 +28,7 @@
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.Version;
+import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.ActionListenerResponseHandler;
 import org.elasticsearch.action.support.PlainActionFuture;
 import org.elasticsearch.cluster.node.DiscoveryNode;
@@ -2786,7 +2787,7 @@ public <T extends TransportResponse> void sendRequest(
             serviceC.connectToNode(
                 serviceA.getLocalDiscoNode(),
                 ConnectionProfile.buildDefaultConnectionProfile(Settings.EMPTY),
-                new ActionListener<>() {
+                new ActionListener<Void>() {
                     @Override
                     public void onResponse(final Void v) {
                         latch.countDown();