Browser security has gone nuts. Anything that the browser doesn't recognise, it flags as a virus. This is extremely stupid and counterproductive because we'll get so used to overriding it that any protection it offers becomes useless.
Download anyway, do a custom scan with the antivirus you've got, or check it online with Virustotal. You can even open the file inside with Notepad and see that it isn't doing anything suspicious, like downloading a malicious payload.