Upgrade dependencies

[curran]

The npm redis package is now at v.2.7.1, and this package is depending on version "^2.6.0".

Would a PR that upgrades the dependencies be welcome?

[houshuang]

@curran Who do we need to ask to get this done? NPM redis dependency is now two years old, but I don't think the API has changed, just speed etc. We're planning to use redis in our project for other things, and I would prefer avoiding bundling two versions of node-redis...

[curran]

@houshuang I believe the only people who can merge PRs here are @rkstedman and @nateps . Perhaps we can convince them to look at #5.

There is some other related activity that may merit a new release of sharedb-redis-pubsub anyway - see share/sharedb#201

[curran]

Closed in #9

Thanks @nateps !