Upgrade Node.js and dependent packages to the latest version

[yhatt]

Notable changes

• Marpit framework has been bumped to v2.6.1.
  • cssContainerQuery constructor option (#355, #377)
  • By another pull request, we are going to enable it in Marp Core by default.
  • lang global directive and constructor option (#376)
• rollup has been bumped major version to v4.
  • It's no longer compatible with Node.js v16 and eariler versions.
  • rollup is devDependencies so we can still use it for development.
• github-markdown-css has been bumped minor version.
  • The regenerated style has applied slightly changed color scheme on GitHub. Thus, default theme also has updated color(s).

Deferred changes

• highlight.js has a new minor version v11.9.0.
  • highlight.js v11.9.0 drops support for Node 14.x.
  • Marp Core is still cover EoL Node.js v14 so should not update to the latest.