Make webpack a peer dependency so users can opt to use webpack 2

[rvaidya]

As a peer dep, we can use whatever webpack version we want as long as it's above the minimum required version

https://github.com/rvaidya/serverless-webpack/tree/peerdep

[thenikso]

cool! could you open a PR to merge that change?

[utkuturunc]

Any updates on this?

[nikolasleblanc]

@rvaidya Jumping in here, any action on that PR?

[HyperBrain]

Released with version 2.0.0