A nasty workaround for a problem which should not exist in the first place. Ditto dependencies on private repositories.
In Go I believe they use the term "idiomatic." ;-)
Would you argue that there are more robust solutions in the Haskell ecosystem? What scheme do you prefer?
This is because Go doesn't support specifying branches/tags itself when specifying a git dependency.
This workaround is contingent on gopkg.in people keeping their service maintained and running. If they went down, all your dependencies would break.