Support 2.12

[sksamuel]

2.12 is moving along nicely and I think its time I updated this compiler plugin to work with 2.12

[sksamuel]

Current status: 2.12 build as 6 failing tests

[mosesn]

Just wanted to check in, what's the status on the 2.12 build these days?

[gheine]

+1

[paulp]

#177

[gslowikowski]

Version 1.3.0-RC1 with Scala 2.12.0-RC1 support released.

[SethTisue]

Could you add it to https://github.com/scala/make-release-notes/blob/2.12.x/projects-2.12.md ?

[gslowikowski]

Done in scala/make-release-notes#185, but I added sbt-scoverage plugin, not scalac-scoverage-plugin because scalac plugin shouldn't be added by the user directly.