chore(Language Translator V3): Update example

Author: mediumTaj

examples/IBM.Watson.LanguageTranslator.v3.Examples/ServiceExample.cs

@@ -224,6 +224,7 @@ public void TranslateDocument()
                     fs.CopyTo(ms);
                     result = service.TranslateDocument(
                         file: ms,
+                        filename: Path.GetFileName(documentToTranslatePath),
                         fileContentType: "text/plain",
                         modelId: "en-es"
                         );