Migration Example minor update

[deBhal]

In the migration example, the "before" includes a default value that we should really include in the after.

I've also tried to update the text around it to match in a separate commit (bc4d0e8), because it's more subjective. I'm fine with changing or dropping those textual changes.

[kadamwhite]

Going to merge this although the page itself is largely out of date, as we didn't make a specific changes page for the 4.7 merge. Thanks for the docs contribution!