Fix missing +/- prefixes in migration diff for v1.39.0.md

[sshine]

Improves readability when migrating to v1.39.0

Description of the change:

In the v1.39.0 migration guide, the section

 github.com/onsi/ginkgo/v2 v2.17.1
 github.com/onsi/gomega v1.32.0
 k8s.io/api v0.30.1
 k8s.io/apimachinery v0.30.1
 k8s.io/client-go v0.30.1
 sigs.k8s.io/controller-runtime v0.18.4
 github.com/onsi/ginkgo/v2 v2.19.0
 github.com/onsi/gomega v1.33.1
 k8s.io/api v0.31.0
 k8s.io/apimachinery v0.31.0
 k8s.io/client-go v0.31.0
 sigs.k8s.io/controller-runtime v0.19.0

now looks like:

- github.com/onsi/ginkgo/v2 v2.17.1
- github.com/onsi/gomega v1.32.0
- k8s.io/api v0.30.1
- k8s.io/apimachinery v0.30.1
- k8s.io/client-go v0.30.1
- sigs.k8s.io/controller-runtime v0.18.4
+ github.com/onsi/ginkgo/v2 v2.19.0
+ github.com/onsi/gomega v1.33.1
+ k8s.io/api v0.31.0
+ k8s.io/apimachinery v0.31.0
+ k8s.io/client-go v0.31.0
+ sigs.k8s.io/controller-runtime v0.19.0

as intended.

Motivation for the change:

To make the migration steps easier to read.

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• Add or update relevant sections of the docs website in website/content/en/docs

I haven't added a changelog entry. Let me know if I should.

[acornett21]

Hi @sshine thanks for the contribution. A changelog entry isn't needed for this, but you will need to sign-off your commit to get the DCO check to pass. More on that below
https://github.com/operator-framework/operator-sdk/pull/6975/checks?check_run_id=46652890495

[sshine]

Done. Ironically, since I switched from a web commit to an --amended commit om my computer, it lacks my cryptographic signature now. ;-)