[Temporal] accept colon in the timezone offset

This is valid in ISO 8601

http://www.w3.org/TR/NOTE-datetime
https://en.wikipedia.org/wiki/ISO_8601#Times
[Temporal] accept timezone offsets with only hours

specifying the minutes is optional
eg. 2014-07-09T01:50:05+12 is a valid ISO 8601 timestamp
Merge pull request #285 from carbin/nom

[Temporal] accept colon in the timezone offset