node 18.x compatibility

Same code that runs fine on node 16.x (basic mg.messages.create) fails on node 18.x with following error

TypeError: fetch failed
    at Object.processResponse (node:internal/deps/undici/undici:5575:34)
    at node:internal/deps/undici/undici:5901:42
    at node:internal/process/task_queues:140:7
    at AsyncResource.runInAsyncScope (node:async_hooks:202:9)
    at AsyncResource.runMicrotask (node:internal/process/task_queues:137:8) {
  cause: TypeError: object2 is not iterable
      at action (node:internal/deps/undici/undici:1661:39)
      at action.next (<anonymous>)
      at Object.pull (node:internal/deps/undici/undici:1709:52)
      at ensureIsPromise (node:internal/webstreams/util:172:19)
      at readableStreamDefaultControllerCallPullIfNeeded (node:internal/webstreams/readablestream:1884:5)
      at node:internal/webstreams/readablestream:1974:7
}

node: 18.1.0 mailgun.js: 6.0.1

[epaminond]

@sholladay , you can try this code to reproduce an error: https://github.com/epaminond/mailgun-error-repro Basically error occurs even if you don’t supply correct MAILGUN_API_KEY and MAILGUN_DOMAIN. Hope this helps!

CC @olexandr-mazepa

[zacharytyhacz]

Interesting, I wonder why they don’t just use fetch or axios