Bump packages

At least those whose upgrade won't require too many code changes.

Cannot update:
- got -- missing cjs support after v12: https://github.com/sindresorhus/got/releases/tag/v12.0.0
- gulp-autoprefixer -- missing cjs support after v9: https://github.com/sindresorhus/gulp-autoprefixer/releases/tag/v9.0.0