Dep is not yet supported by client-go as of v6.0.0. It is possible to manually make a Gopkg.toml that overrides every single dependency of client-go if you absolutely need to use dep. But it's not really worth the work.
This folder does include a sample Gopkg.toml that was made by converting the the GoDeps.json to a set of overrides. Removing duplicates and targeting root package names. It was a pain to generate and would have to be manually updated for each client-go upgrade. But it is possible to do.