fix JSONFeed Hubs

[wybiral]

Fixes: JSONFeed.Hubs attribute was of type []*JSONItem when it should have been []*JSONHub.

Summary of Changes

1. Changed type of JSONFeed.Hubs from []*JSONItem to []*JSONHub.

[elithrar]

Thanks - can you add a test that covers this?

[wybiral]

Sure, b194c17 will make sure that the type is correct and that JSONFeed serializes correctly with hubs.

This change doesn't impact other feed types since this package doesn't support hubs for them (although technically Atom feeds can support hubs using links with rel="hub" which could translate to JSONFeed).

[elithrar]

Perfect; thanks @wybiral!