HTML Markup Error

Your Plugin is really nice, I like it!

I just did an HTML-Validation of my site and was surprised to get some errors. They are caused by the script tags that include the minified js-files.
<script type='text/javascript' src='https://...' defer='defer''></script>
Notice the double single quote at the end of the defer attribute.

The defer option is checked and this is the only setting I have changed.
Do you think this is an error caused by your plugin? Can you reproduce this behaviour?

https://www.ads-software.com/plugins/fast-velocity-minify/