fix: revert exports syntax change

[bjornstar]

Resolves #179

The exports syntax that was used in v5.4.0 only works in node v20+

Reverting it back to the previous syntax fixes the problem, but I tried to test it with node v20 and ran into an error:

npx ts-node-esm ./index.ts
TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /Users/bjornstar/test/index.ts

This seems to be an issue with ts-node in node v20 - TypeStrong/ts-node#1997
With a WIP PR from isaacs - TypeStrong/ts-node#2009

In the meantime there is a workaround to use the ts-node/esm loader directly:

node --no-warnings=ExperimentalWarning --loader ts-node/esm ./index.ts

It would be nice if we could unblock existing node v16 / v18 users until ts-node is fixed on node v20.

[sindresorhus]

The exports syntax that was used in v5.4.0 only works in node v20+

This is incorrect. That syntax has worked since Node.js v12. The problem here is TypeScript.

[sindresorhus]

I will revert it for now. But it will come back in the next major version.