snap: Bump bundled Node.js from v12.18.3 to v12.18.4
snap: Bump bundled Node.js from v12.18.3 to v12.18.4

due to CVE-2020-8201, CVE-2020-8251 and CVE-2020-8252,
see https://nodejs.org/en/blog/vulnerability/september-2020-security-releases/

anthonyfok/hugo,anthonyfok/hugo,anthonyfok/hugo,gohugoio/hugo,gohugoio/hugo,gohugoio/hugo