chore(deps): Bump markdown-it, @vuepress/plugin-docsearch, vuepress, vuepress-plugin-seo2 and vuepress-plugin-sitemap2 in /docs

chore(deps): Bump markdown-it, @vuepress/plugin-docsearch, vuepress, vuepress-plugin-seo2 and vuepress-plugin-sitemap2 in /docs #1959