All dependencies are committed in the vendor folder, so gophy is go get-able, and you don't need any extra tool to develop gophy,
however, gophy uses gvt to manage and update it's dependencies, so it is advised to use it when
dealing with dependencies (but feel free to add/update the entry in the vendor/manifest file by hand, if you're so inclined).
To install gvt simply run: go get -u github.com/FiloSottile/gvt