deps: update npm to 2.13.1
Hey! Here's a new npm for you. We figured you'd rather get it on Monday than Friday. :) You can check out the release notes here: https://github.com/npm/npm/releases/tag/v2.13.1
Mostly minor bugfix and internal stuff (docs, deps, refactor, test) bits.
r: @Fishrock123 r: @chrisdickinson