EPUB cannot be deleted while the EPUB-Checker is opened

Due to https://github.com/w3c/epubcheck/pull/1547, the `java.util.zip.ZipFile`-object used for the checks is not closed immediately after the check and so the EPUB file cannot be edited, deleted, or overwritten. I created [a pull request](https://github.com/w3c/epubcheck/pull/1547) and I am waiting for it to be merged into [w3c/epubcheck](https://github.com/w3c/epubcheck).