Getting "clean_css_1.default is not a constructor" errors on latest release

[FreekVR]

Since the lastest release (4.2.2) I'm getting errors due to an apparent issue with the clean_css usage:

[!] (plugin VuePlugin) TypeError: clean_css_1.default is not a constructor
src/components/layout.vue
TypeError: clean_css_1.default is not a constructor
    at initializer (/home/freek/projects/styleguide/node_modules/@vue/component-compiler/dist/postcss-clean.js:6:19)
    at Object.creator (/home/freek/projects/styleguide/node_modules/@vue/component-compiler/node_modules/postcss/lib/postcss.es6:111:27)
    at SFCCompiler.doCompileStyle (/home/freek/projects/styleguide/node_modules/@vue/component-compiler/dist/compiler.js:133:42)
    at SFCCompiler.<anonymous> (/home/freek/projects/styleguide/node_modules/@vue/component-compiler/dist/compiler.js:116:47)
    at Generator.next (<anonymous>)
    at /home/freek/projects/styleguide/node_modules/@vue/component-compiler/dist/compiler.js:7:71
    at new Promise (<anonymous>)
    at __awaiter (/home/freek/projects/styleguide/node_modules/@vue/component-compiler/dist/compiler.js:3:12)
    at SFCCompiler.compileStyleAsync (/home/freek/projects/styleguide/node_modules/@vue/component-compiler/dist/compiler.js:115:16)
    at Object.<anonymous> (/home/freek/projects/styleguide/node_modules/rollup-plugin-vue/dist/rollup-plugin-vue.js:271:57)
    at Generator.next (<anonymous>)
    at /home/freek/projects/styleguide/node_modules/rollup-plugin-vue/dist/rollup-plugin-vue.js:33:71
    at new Promise (<anonymous>)
    at __awaiter (/home/freek/projects/styleguide/node_modules/rollup-plugin-vue/dist/rollup-plugin-vue.js:29:12)
    at Promise.all.descriptor.styles.map (/home/freek/projects/styleguide/node_modules/rollup-plugin-vue/dist/rollup-plugin-vue.js:267:87)
    at Array.map (<anonymous>)

If I use the yarn "resolutions"-field to downgrade to 4.2.1, the issue disappears. Alternatively, removing the "default"-suffix from "clean_css_1" in node_modules/@vue/component-compiler/dist/postcss-clean.js also fixes the issue on 4.2.2

[znck]

Fixed in #103