Treat the environment during webpack build as browser rather than node

[carlobeltrame]

Fixes #47

I need some help to set up tests for this. I was unable to run the tests locally, since on my local machine, I have installed neither grunt nor python (required for the npm package sleep, which is an optional dependency of karma-xvfb-chrome-launcher) nor java (required for mockserver) nor Chrome (I am running on Ubuntu). Rather, I use all those only in Docker containers when necessary.

I think a useful testing setup would require a new grunt task, like the ones you have set up for node and browser modes. We could take the easy way out and just copy the browser tests and define a global require mock before the tests. Or we could do it the completely correct way and somehow set up a Webpack environment within the tests, similar to how you start an entire browser for the browser tests. Both of these options go a little far given the superficial knowledge I have about this package's structure and build process.

[carlobeltrame]

Sorry about the failing build! And thanks for the quick fix.