Possible to parse dates as UTC?

[blakeembrey]

Currently dates are always parsed in the local timezone, but since that changes it's unlikely to be what you'd actually want. Would you be willing to accept a PR for working with dates in UTC so it'd always serialise to the same time across timezones?

Relevant source code: https://github.com/devongovett/exif-reader/blob/master/index.js#L132-L149