Eliminate webpack build

[mattbishop]

Given js.spec is a node module, nobody is going to <script> it into a browser directly. Instead they will use their own packaging toolchain to do so like browserfy or webpack. Js.spec doesn't need to create a webpacked build.

Not doing so will also increase the understandability of stack traces and the project in general.

[arichiardi]

I agree with this, consumers will do whatever they basically need to make it work and I see no other big lib provides a build directly.

@prayerslayer any objection? thoughts?