Errors in tests appearing for Node.js >= v10.14.2
[Something that changed between Node.js v10.14.1 and v10.14.2](https://github.com/nodejs/node/blob/master/doc/changelogs/CHANGELOG_V10.md#10.14.2) has caused errors to log in a few places in tests (which still pass):

https://travis-ci.org/jaydenseric/graphql-upload/jobs/477605581#L570

```
Error: Parse Error
      at socketOnEnd (_http_server.js:455:20)
      at Socket.emit (events.js:193:15)
      at Socket.EventEmitter.emit (domain.js:459:23)
      at endReadableNT (_stream_readable.js:1129:12)
      at process.internalTickCallback (internal/process/next_tick.js:72:19)
```

We need to work out if its a bug in Node.js,  or a `graphql-upload` compatibility issue with the new Node.js versions.