Upgrade dependent packages to the latest version

[yhatt]

Notable changes

• Bumped Marpit version to v2.1.1.
• We are continuously making a progress toward dropping End-of-Lifed Node 10 support. We have no longer tested against Node 10 at CI service. Marp Core still should be able to install into Node 10, but may be required --ignore-engines with yarn v1 due to deep dependency commander.
• eslint-plugin-import says complains to @rollup/plugin-node-resolve as same as Upgrade dependent packages to the latest version marp-cli#371.