Error creating compilation of appengine cloud storage in demo project

Following https://cloud.google.com/appengine/docs/go/googlecloudstorageclient/getstarted the deployment fails

goapp deploy -oauth

from

app.go:78: cannot use google.AppEngineContext(c) (type "golang.org/x/oauth2".Option) as type "github.com/golang/oauth2".Option in function argument

I can run the demo project by changing import lines 33-34 in google.golang.org/cloud/examples/storage/appengine/app.go

from

"github.com/golang/oauth2" "github.com/golang/oauth2/google"

to

"golang.org/x/oauth2" "golang.org/x/oauth2/google"

Most importantly, this is the correct way to "fix" this (and should the demo project be / or be updated by Google?) And if anyone has an understanding, if you could provide some context as to why there is (as it seems to me ) multiple ways to reference the same package, which would be great.