Update the dependency `http-errors` to v2

The dependency `http-errors` is a major version out of date:

https://github.com/jshttp/http-assert/blob/b072a1b903d055a7d40dbd7a54cd74e517b56e52/package.json#L13

This is causing problems with multiple versions of HTTP errors floating around codebases, where some are not `instanceof` each version's HTTP error class.