Edited upload.php example in README file

[roibeart]

I changed the example for the upload.php file because in my opinion could be confusing: it uses the getIdentifier() method to give a name to the uploaded file, which produces a file without an extension and which is not intended for naming files, as suggested to me here.

[coveralls]

Coverage remained the same at 100.0% when pulling c716bbb on roibeart:roibeart-readme-edit into 340ed5b on flowjs:master.

[AidasK]

Thanks