ES module support

[socketopp]

I am getting this error:

[!] (plugin postcss) Error: require() of ES Module \postcss.config.js from 
node_modules\lilconfig\dist\index.js not supported.
Instead change the require of postcss.config.js in \node_modules\lilconfig\dist\index.js to a dynamic import() which is available in
all CommonJS modules.

See similar error in postcss-cli.
postcss/postcss-cli#387

[easonlin-Dashmote]

How about renaming postcss.config.js to postcss.config.mjs? Works for me.