jimp.read is failing silently in a grunt task

# Expected Behavior

When you call `jimp.read`, then `jimp.read.then` or `jimp.read.catch` are called.

# Current Behavior

If `jimp.read` is called in a grunt task, then neither `jimp.read.then` or `jimp.read.catch` are called. If you call `jimp.read` in the node repl or in a node script, it works normally.

```
$ node
Welcome to Node.js v13.7.0.
Type ".help" for more information.
> var test = require( './test' );
undefined
> test();
attempting resize
running resize task
Promise { undefined }
> jimp.read success
image processing success!
received buffer, great news!

>
(To exit, press ^C again or ^D or type .exit)
>
$ grunt test
Running "test" task
Resizing
attempting resize
running resize task

Done.
$
```

# Failure Information (for bugs)

See above.

## Steps to Reproduce

$ git clone https://github.com/mattpen/jimp-grunt-test.git
$ cd jimp-grunt-test
$ npm install
$ grunt test

**Screenshots**

N/A, either an image is generated or it isn't.

## Context

- Jimp Version: 0.9.5
- Operating System: MacOS 10.14.6
- Node version: 13.7.0

## Failure Logs

No log output was produced by jimp.

Start by reproducing the failure with the linked mattpen/jimp-grunt-test project using Node.js 13.7.0, Jimp 0.9.5, and `grunt test`, then compare it with the Node REPL or script behavior described here. Done means the `jimp.read` promise settles during the Grunt task and the expected image output or failure is observable.

Written by the indexing model from the issue text.