go get instructions need updating

[gdbelvin]

The rules for using go modules have changed in go 1.13.
When running go get from outside a directory with a module file, go reverts to pulling everything from head.

go get upspin.io/cmd/...
# golang.org/x/crypto/acme/autocert
go/src/golang.org/x/crypto/acme/autocert/autocert.go:76:16: undefined: idna.Lookup
go/src/golang.org/x/crypto/acme/autocert/autocert.go:263:15: undefined: idna.Lookup
# upspin.io/upspin/proto
go/src/upspin.io/upspin/proto/upspin.pb.go:52:11: undefined: proto.ProtoPackageIsVersion2
go/src/upspin.io/upspin/proto/upspin.pb.go:598:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:599:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:600:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:601:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:602:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:603:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:604:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:605:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:606:2: undefined: proto.RegisterType
go/src/upspin.io/upspin/proto/upspin.pb.go:606:2: too many errors

Please change to

GO111MODULE=on go get upspin.io/cmd/...
go: finding upspin.io latest
go: downloading upspin.io v0.0.0-20200124224713-5ddde7b8e6ff
go: extracting upspin.io v0.0.0-20200124224713-5ddde7b8e6ff
go: downloading golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3
go: downloading gopkg.in/yaml.v2 v2.2.2
go: downloading github.com/NYTimes/gziphandler v0.0.0-20170916004738-97ae7fbaf816
go: downloading golang.org/x/text v0.3.0
go: extracting gopkg.in/yaml.v2 v2.2.2
go: downloading github.com/russross/blackfriday v0.0.0-20171011182219-6d1ef893fcb0
go: downloading golang.org/x/crypto v0.0.0-20191117063200-497ca9f6d64f
go: downloading bazil.org/fuse v0.0.0-20160811212531-371fbbdaa898
go: downloading github.com/golang/protobuf v0.0.0-20171021043952-1643683e1b54
go: extracting github.com/NYTimes/gziphandler v0.0.0-20170916004738-97ae7fbaf816
go: extracting bazil.org/fuse v0.0.0-20160811212531-371fbbdaa898
go: extracting github.com/russross/blackfriday v0.0.0-20171011182219-6d1ef893fcb0
go: extracting golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3
go: extracting github.com/golang/protobuf v0.0.0-20171021043952-1643683e1b54
go: extracting golang.org/x/crypto v0.0.0-20191117063200-497ca9f6d64f
go: extracting golang.org/x/text v0.3.0
go: finding golang.org/x/crypto v0.0.0-20191117063200-497ca9f6d64f
go: finding bazil.org/fuse v0.0.0-20160811212531-371fbbdaa898
go: finding github.com/NYTimes/gziphandler v0.0.0-20170916004738-97ae7fbaf816
go: finding github.com/russross/blackfriday v0.0.0-20171011182219-6d1ef893fcb0
go: finding golang.org/x/text v0.3.0
go: finding gopkg.in/yaml.v2 v2.2.2
go: finding github.com/golang/protobuf v0.0.0-20171021043952-1643683e1b54
go: finding golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3

[gdbelvin]

Related: google/keytransparency#1450

[u0nel]

shouldn't it be go install upspin.io/cmd/...@latest?