Bumps [prismjs](https://github.com/PrismJS/prism) from 1.20.0 to 1.21.0. - [Release notes](https://github.com/PrismJS/prism/releases) - [Changelog](https://github.com/PrismJS/prism/blob/master/CHANGELOG.md) - [Commits](https://github.com/PrismJS/prism/compare/v1.20.0...v1.21.0) Signed-off-by: dependabot[bot] <support@github.com>