Invalid resource error handling

[narkq]

In a server-side fetcher, there is currently no way to handle any error that's thrown by Fetcher.getService (since it gets executed via setImmediate inside of a promise constructor).
In particular, if you specify an invalid resource name (and that's easy to do for the new people on team in a substantially complex app), an error ends up in uncaughtException handler (or crashes the server).

[yahoocla]

CLA is valid!

[coveralls]

Coverage increased (+0.02%) to 97.204% when pulling b37b8ab on narkq:invalid-resource-error-handling into 55d520f on yahoo:master.

[lingyan]

👍

[redonkulus]

👍

[lingyan]

Thanks @narkq for your contribution!
New release has been published with your fix: https://github.com/yahoo/fetchr/releases/tag/v0.5.30