upgrade dependencies to fix vulnerability

[fuzetsu]

Hi, thanks for this tool, just what I needed 😄

I was getting some npm audit errors through this package because of semver: https://www.npmjs.com/advisories/31

While fixing that I took the chance to update all the dependencies (hopefully that's alright).

The tool still seems to work, and the tests all pass (with a small tweak, looks like .falsy went away at some point).

I didn't look in detail to see what changed in chai/mocha/sinon in those major versions, but the tests pass and there weren't any warnings/errors in the console so I think we're OK 😅

[rstacruz]

Thanks! Just released this onto npm.