Update default value in Java snippet

`@Default.String("gs://my-bucket/input")` was used as the default value for both the input and the output custom option.

website/src/documentation/programming-guide.md

@@ -227,7 +227,7 @@ public interface MyOptions extends PipelineOptions {
     void setInput(String input);
 
     @Description("Output for the pipeline")
-    @Default.String("gs://my-bucket/input")
+    @Default.String("gs://my-bucket/output")
     String getOutput();
     void setOutput(String output);
 }