fix(go.mod): fix module path

[holmanb]

Fixes #240
Fixes #267

[holmanb]

Note to reviewers: Install documentation was broken by the change from #238. This updates the code to match the documentation.

An alternative proposal, #260 reverts the offending commit - however this doesn't address other issues related to printing links that 404.

[niemeyer]

Thanks for fixing these.

[holmanb]

With the updated go.mod, the documented install command now works:

$ go install github.com/canonical/spread/cmd/spread@latest
go: downloading github.com/canonical/spread v0.0.0-20260323164801-a3a44a96b6d0
go: downloading github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e
go: downloading golang.org/x/oauth2 v0.25.0
go: downloading github.com/go-goose/goose/v5 v5.0.0-20230421180421-abaee9096e3a
go: downloading golang.org/x/net v0.38.0
go: downloading golang.org/x/crypto v0.36.0
go: downloading golang.org/x/term v0.30.0
go: downloading gopkg.in/tomb.v2 v2.0.0-20161208151619-d5d1b5820637
go: downloading gopkg.in/yaml.v2 v2.4.0
go: downloading golang.org/x/sys v0.31.0
go: downloading cloud.google.com/go/compute/metadata v0.3.0
go: downloading github.com/kr/text v0.2.0
go: downloading github.com/juju/collections v0.0.0-20220203020748-febd7cad8a7a

Thanks for fixing these.

Welcome, and thanks for merging.