support timezone without a colon (:) character

[bxparks]

Currently, the optional timezone indicator on a TIMESTAMP field is expected to contain a colon (:) character. For example:
2017-05-22 12:33:01-07:30

However, ISO8601 allows a timezone format without the colon character, like this:
2017-05-22 12:33:01-0730

I have not needed this feature yet, but this should be easy to add if someone needs it.