Update Gopkg.lock for dep 0.5.0 (#398)

* Update Gopkg.lock for dep 0.5.0

This adds changes to Gopkg.lock generated by running `dep ensure` with
dep version 0.5.0. Mostly, the changes are addition of extra information
for vendor verification.

* Update user-guide and README with dep 0.5.0 prereq

Author: darkowlzz