set the default branch as the current latest release of slick

[He-Pin]

eg,here,it should be set to slick3.1

[jrovu]

Agreed. As a new Scala/Play user, this is especially confusing.

[smootoo]

Hopefully this PR makes things a little clearer #22

[jodersky]

The PR is a good start, however I think changing the default branch to 3.1.1 would be even better? It's very confusing for people coming from a search engine.

[cvogt]

@szeiger @corruptmemory is there an activator reason for this?

[jodersky]

I actually found this repo through the activator template page. The page says the template is for slick 3.1, however it redirects to master which is for and older version.
It was quite confusing, hence my comment above (I was also pretty tired though, so it may not be as bad ;) )