Running "dep ensure" no longer always writes out the Gopkg.lock file.
As such if somehow Gopkg.toml has a newer modified time than Gopkg.lock
the make command would always run "dep ensure" and all other build
steps.
This change makes it explicit that after a dep ensure run that
Gopkg.lock is newer than Gopkg.toml.
Nathaniel Cook
j. Emrys Landivar (docmerlin)