superjson.registerCustom is not defined when "type": "module"

[converter-user-old]

When i use "type": "module" in my package.json i get a error that the function is not defined.
Only if i use superjson.default.registerCustom then it works but TS will then complain.

See https://codesandbox.io/s/reverent-dream-4khu8b

[Skn0tt]

@all-contributors please add @ruessej for bug

[allcontributors]

@Skn0tt

I've put up a pull request to add @ruessej! 🎉

[Skn0tt]

released in 1.9.1! thank you @ruessej :)