Shrink dependency graph by pruning Node 4 things

[Krinkle]

I noticed that GoogleChrome/puppeteer has an indirect dependency on isarray, which is coming in through extract-zip. See https://npm.anvaka.com/#/view/2d/puppeteer/1.11.0.

The chain is:

puppeteer@1.11.0
> extract-zip@1.6.7
> concat-stream@1.6.2
> readable-stream@2.3.6
> isarray

The latest versions of puppeteer, extract-zip, contact-stream and readable-stream only support Node 6 and above.

• readable-stream 3.0 no longer depends on isarray.
• concat-stream 2.0 uses readable-stream 3.0.

The next step is for extract-zip to use concat-stream 2.0, and publish a release.