Ignore benchmark directory in the npm package

[gustavohenke]

It seems like we're packaging the benchmarks within the npm package:

Not a super weighty directory, but it's a best practice to not install something that the end-user is not going to use.

[novacrazy]

Pretty sure it can be fixed by just adding a new line benchmarks/ to the .npmignore file, bumping the version a tiny bit and republishing.

[gustavohenke]

Yes, sure! I created this issue as a reminder for any of us.