[DShop] Upgrade TailwindCSS module to v. 2.0 or higher

By default, HTML headings are "unstyled" by TailwindCSS. A plugin (@tailwindcss/typography) can be used to get around this limitation, but recent versions of the plugin require an upgrade of the TailwindCSS module by a 'major' version (v 1.x to v 2.x). TailwindCSS is used by all of DShop's current themes to style components. An upgrade of this module (to version 2.0 or higher) comes with a "handful of breaking changes" that are documented here: https://tailwindcss.com/docs/upgrading-to-v2