Update pg to 2.5.x

Update: now mergable.

One oddity that arises from this change is that datetimes *may not* survive round trips.

The reason is because when datetimes are saved, they're saved in UTC. When they're reified, the date object has the correct time, but in the wrong timezone. So the tests fail. Sometimes. I've managed to get them failing with Postgres.app on Mac OSX, but they'll pass on Travis' machines.

I can't understand what is going on, was hoping @mde had some insight from writing timezone.js

Here is the relevant code in the `pg` module: https://github.com/brianc/node-postgres/blob/84af374ab7024f13815686c6b1dbeb07e599a6b9/lib/types/textParsers.js#L37.