Update PG library

[AndyMathys]

Hello,

I'm currently running this lib in production and am running into some issues after an update of our node version.

The current used version of pg will not work on node 6 or node 7 due to this issue brianc/node-postgres#1000

This update makes the node-pg-jobs lib usable under newer node versions.

[timlesallen]

Thanks heaps @AndyMathys. I wanted to update travis as well so I've done a separate PR which should have the changes you want. It's merged and published. Thanks for your contributions. Interestingly the tests all pass before/after the upgrade to pg@6... What was broken exactly?

[AndyMathys]

Thanks for the update, just redeployed with the latest version and it's working great again.

Before the update the library was unable to connect to the PG server when using a connection string and would fail with error message "password authentication failed for user xxx" as described in this PG issue brianc/node-postgres#1000

I'm not sure if this was only the case for complex connection strings or for all of them.

[timlesallen]

@AndyMathys Ah, I see. Btw, I've given you commit access to the repo... See https://github.com/noblesamurai/node-pg-jobs/blob/master/CONTRIBUTING.md for more info.