[update] use newest, exact versions of webpack, karma, et al.

[ltk]

webpack version 1.7.3 and webpack-dev-server version 1.10.1 [didn't get along]([see issue here]%28https://github.com/webpack/webpack/issues/1225%29).(https://s3.amazonaws.com/vigesharing-is-vigecaring/lkurtz/npm_start_node_2015-09-15_15-21-02.png)

This PR updates package.json to the newest versions of these modules. It also starts defining dependencies with exact versions to avoid issues like this moving forward.

There was also an issue with karma that necessitated a version bump along with the webpack modules.

[ltk]

Are we into defining exact versions? If so, should we make them exact as we have need to, or should we proactively change them to be exact?

[nhunzaker]

Yikes. Good call. I am a fan of exact versions. Definitely for development dependencies. I've been doing this on a lot of projects now; I am surprised it isn't in CK already.

For production dependencies, we should be more lenient to avoid duplication. Still, for development we can set exact versions of those dependencies for consistency.

[nhunzaker]

👍