use zipWriter.SetOffset instead of "zip -A"

[boyvinall]

addresses #74

[boyvinall]

I'm not sure why lint failed on https://app.wercker.com/buildstep/58359a0511125f0100d850a1. I'm not familiar with wercker .. doing read of the docs, I thought I could use a docker image as the "box". I built using the wercker CLI tool using this updated wercker.yml but that seems to fail on their cloud environment.

The reason for this PR was I hit an issue with zip -A when trying to run on a vagrant/virtualbox shared host filesystem, it looked like there was some filesystem sync issue. My change seems to help with this... and it also closed one of your issues.

Grateful for any advice you can offer in getting the wercker build running, otherwise I might not get back to this for a while.

[GeertJohan]

Thanks!

[boyvinall]

Glad to help, thanks for merging.