Bump celery version

[tayloramurphy]

The required version of celery is currently at 3.1.11 which is almost 4 years at this point. Similar to #195 , it's causing problems managing virtual environments. I use pipenv and I'm unable to generate a lockfile because of this dependency.

[BenFradet]

Unfortunately, we haven't had a lot of cycles to dedicate to this tracker lately, a PR would be most welcome 👍

[tayloramurphy]

Maybe I'm doing something completely wrong but I'm having a bear of a time even getting the test suite up and running. I made a note in this comment w/in the dbt repo about my difficulties and the changes I've had to make to get it to even do something.

The last thing I ran into was redis wasn't running. At that point I ran out of time to try and poke at this some more. :(

[BenFradet]

hey Anton Parkhomenko (@chuwy) can you somehow help out Taylor A. Murphy (@tayloramurphy) here?

[chuwy]

Sorry to hear about it Taylor A. Murphy (@tayloramurphy). Strangely enough, Redis should be installed on Vagrant machine.