Transform images with sharp (v4)

https://sharp.pixelplumbing.com/

```js
sharp(input)
  .resize(200, 200, {
    fit: sharp.fit.inside,
    withoutEnlargement: true
  })
  .toFormat('jpeg')
  .toBuffer()
  .then(function(outputBuffer) {
    // outputBuffer contains JPEG image data
    // no wider and no higher than 200 pixels
    // and no larger than the input image
  })
```