fix: correct $segment for PopulateTask per docs

[wilr]

@GuySartorelli as per silverstripe/silverstripe-staticpublishqueue@2f05ec1 it looks like this class was upgraded without one defined but the documentation refers to the old version. To review if we should mark this as a API change before merge. I don't think this would be as drastic as the above one since it's unlikely anyones running it in production (only perhaps for demo sites)

[GuySartorelli]

IMO This is a breaking change and will need to target a new major branch once one is created.
For whatever reason, the master branch in this repository is actually the branch for the current major line, so breaking changes can't be introduced to it.

That said, like you've pointed out there's a much lower chance of this being run in production than the queued jobs module so I'll let someone else make the call.

[michalkleiner]

The repo was originally DNA's so I think the master branch situation is a remnant of the transition to silverstripe org not having a major line branch created.
I'm happy to merge the PR since the change is not changing any functionality and the adoption of the module is probably reasonably small, more so its use in production.

[madmatt]

Yep I agree with @michalkleiner, merging this now.