Use a node-based proxy instead of browsermob-proxy

[dontcallmedom]

This is not backwards-compatible with the current version of the API; I have a separate update to w3c/Mobile-Checker to account for that that I'll submit once the npm version of this is available.

[gbaudusseau]

I get the same error as the travis build.

[tripu]

@dontcallmedom, what is the status of this?

Will this PR solve these issues with the Travis builds, namely having to use sudo?

[tripu]

@dontcallmedom, your travis-setup.sh is “inspired from https://github.com/web-animations/web-animations-js/blob/master/.travis-setup.sh”, but that script isn't working on Travis either, right? (I was looking at it to see if those guys had solved this issue with sudo…)