Go jxl mime not serverd correctly

How to reproduce

1. Clone this repo
2. run go run main.go
3. In safari/jxl supported browser open http://localhost:3000/logo.jxl browser will prompt to download instead of displaying in browser
4. On the other hand jpeg or any Go supported mimetype are displayed in browser.

Why this happens?

.jxl files are not served with right mimetype