Report which route failed during pre-rendering.

[JeanMeche]

Description

While build a pre-rendered app, I'm greeted with the following error :

Exception:
UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<ne>".
ERROR

This error makes it hard to investigate the cause as it only happens during pre-rendering (dev mode serve is fine).

It'd be great to have some details, like for example which route is throwing while being pre-rendered.