Change access to direct implementation

The example code wasn't accessing the factory that was explicitly created for this interface. It was instantiating the implementing class directly from the impl package.

README.md

@@ -76,7 +76,7 @@ FluentArguments arguments = ArgumentListBuilder.builder()
                                                .add("unreadEmails", 5)
                                                .build();
 
-System.out.println(bundle.resolveMessage("emails", arguments, new StringResultBuilder()).get());
+System.out.println(bundle.resolveMessage("emails", arguments, StringResultFactory.construct()).get());
 ```
 
 ```console