Cannot subclass errors

[cdignam-segment]

I was surprised I couldn't subclass errors. I would have expected my ValidationError class would support an instanceof check against itself.

const { BadRequest } = require('http-errors')
const assert = require('assert')


class ValidationError extends BadRequest {}

const err = new ValidationError()
console.log(err.name)
// "BadRequestError"

// err should be an instance of ValidationError
assert(err instanceof ValidationError)

https://runkit.com/cdignam-segment/6536e492c20c690008824a73

[jonchurch]

duplicate of #98, but yes duly noted. I would expect this to work this way as well.