There should be no reason to use gopkg.in versioned imports now that
we're using go modules. I think, IANAE.
gopkg.in kind of gets in the way of modules, as it only pulls over
tagged releases from github.com -- this then means that you need to use
go modules 'replace' syntax in the go.mod to use a non-versioned commit
or branch. This is feasible, but kind of ugly.
go modules defaults to pulling the latest version, so the default
behavior is the same as when pulling go-jira.v1 from gopkg.in.
Keien Ohta