Release for 2.12.8

[clhodapp]

Not a huge deal but it would be very helpful because constraint-solving with macro-paradise means that unless a 2.12.8 is released, users of both are stuck on 2.12.2.

Ref #180

[oscarvarto]

Asking for a 2.12.7 release here, Instead of opening a new ticket...

Is there any hope to get a new release? It's been more than a year since last release 😞

[SethTisue]

note that we (Lightbend) expect to build 2.12.8 later this month

[oscarvarto]

Well, 7 months ago, you @SethTissue #180 (comment)
presented a similar argument, and it seems that it is never a good time to get a new release for typelevel scalac...

And we could keep waiting forever :/