bug: when no repository prefix is specified, docs "see code" is not generated

[Aghassi]

https://github.com/oclif/dev-cli/blob/9c9be3dff5e063b9ce06feb700c79317a6e84e21/src/commands/readme.ts#L180

We are on an enterprise GitHub instance, and by default we are not getting the See code path/to/file.js. It looks like pjson.oclif.repositoryPrefix is undefined, causing this logic to break and always return. Still digging into it, but it seems like it should default to false instead of undefined if nothing is provided...