Upgrade to RxJava 1.1.5

After the fix for ReactiveX/RxNetty#509 we can remove the workaround
to concatenate with an empty Observable for the request body and
upgrade to the latest RxJava 1.1.5.

Issues: #103

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/RxNettyServerHttpRequest.java

@@ -93,9 +93,7 @@ public class RxNettyServerHttpRequest extends AbstractServerHttpRequest {
 
 	@Override
 	public Flux<DataBuffer> getBody() {
-		Observable<DataBuffer> content =
-				this.request.getContent().map(dataBufferFactory::wrap);
-		content = content.concatWith(Observable.empty()); // See GH issue #58
+		Observable<DataBuffer> content = this.request.getContent().map(dataBufferFactory::wrap);
 		return RxJava1ObservableConverter.from(content);
 	}