Default Time Format in FromJSON instance of ZonedTime

In the parsing of zoned times, the time format obtained from defaultTimeLocale is not tried. Many JSON files use this format ([Twitter created_at field](https://dev.twitter.com/docs/platform-objects/tweets), for example) and I think it should be in the list of time formats too.

I added the format in the simplest way. Not sure if any further changes are needed, but currently it works just fine.