Fix datetime zone output.

[mattcoley]

Comparing http://strftime.org/ and https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html, %z should map to Z which outputs the offset +HHMM or -HHMM. %Z should map to z which outputs the shorthand name fo the timezone (for example PDT).

[boulter]

Doesn't this have the potential to break a lot of existing pages that use %Z?

[mattcoley]

I'll have to look at usage for %Z since we have always converted this value incorrectly and received a JIRA about it being incorrect a year ago. I am guessing it is not widely used if this bug has only been reported twice.