Consider switching to nyc from istanbul

[JimiC]

nyc is much easier to work with and since istanbul seems not to be maintained anymore (by the time I'm writing this it's been 7 months without a single commit) it seems prudent to do so.

With nyc the test script will look like this:

    "test": "nyc mocha"

Simple as that.

[eddiemoore]

I agree that nyc is much better than istanbul. Will look into updating

[DiegoRBaquero]

nyc took over, agreed.

[revelt]

+1