Fetch error stack traces are missing in Node

[RobertWHurst]

It seems isomorphic-fetch is using an old version of node-fetch that doesn't render stack traces correctly for their custom fetch error class. I've made a PR to resolve the issue. I suggest either updating isomorphic-fetch if and when the author merges the PR, or relying directly on node-fetch and whatwg-fetch instead.

Example of a stack trace from an ECONNREFUSED error:

[ndelvalle]

Thanks @RobertWHurst I just subscribed to the PR to see if it gets merged.