Add rel attribute to external links
You should add the attribute rel to a link (according to webhint), because the link could "redirect to a phishing website looking like the original ...".
You may use the "noopener" to prevent a security breach (that got patched), and "noreferrer" so that the website opened do not know which website the visitors are coming from. It looks quite useless now, because can use the header (for referrer) and the breach got patched.
<a href="https://webhint.io/docs/user-guide/hints/hint-disown-opener/" target="_blank" rel="noopener noreferrer">webhint</a>