Upgrade pngjs version to 3.3.2

[euxn23]

Upgrade pngjs to 3.3.2, to enable using with node v9.

pngjs/pngjs#95

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[anescobar1991]

This isn't needed as we use the caret(^) and so on any install it will pick up the latest minor or patch version for that package.

Will release in the next few days with this fix and a few other things :)

[anescobar1991]

@euxn23 pngjs still is not fully node v9 compatible, I suggest you open up an issue with them. The following code which simulates where I see it failing in jest-image-snapshot reproduces the issue:

const { PNG } = require('pngjs');
const fs = require('fs')

const image = fs.readFileSync(process.cwd() + '/image-g.png');
PNG.sync.read(image);