Remove Node.js --debug-port / --inspect workaround

[sindresorhus]

When it's fixed in Node.js (nodejs/node#5025) itself and we target that version. So it's going to be a long while until we can. I'm just opening this so we don't forget.

The workaround was introduced in #874.

[sindresorhus]

Sorry, forget to mention — nodejs/node#5025 only about --debug-port=0, but currently no issue about --inspect — please see nodejs/node#5025 (comment) "it should be possible to extend this to --inspect after this PR lands." Currently, --inspect should be used to achieve the best user debug experience (yeah, nodejs 7 is required). - @develar

@develar Could you open an issue on Node.js about the --inspect flag?

[develar]

Blocked on nodejs/node#8080 (--inspect).

[sindresorhus]

The fix landed in Node.js 8.1.0, so we can do this now.

[novemberborn]

I did, in #2096.