Trying to vendor Survey with dep ensure --add github.com/AlecAivazis/survey@2.0.4 yields the message
v2.0.4: "github.com/AlecAivazis/survey" imports "github.com/AlecAivazis/survey/v2/core", which contains malformed code: no package exists at "github.com/AlecAivazis/survey/v2/core"
Sorry to hear you are running into problems with dep. A few people have brought this up and it seems to be a dep issue since they don't support gomodules. Sorry I can't be of much help!
Trying to vendor Survey with
dep ensure --add github.com/AlecAivazis/survey@2.0.4
yields the messagedep version: devel on 1.12.8 go version: 1.13.1