publish against 2.12.0-M5

[adriaanm]

Still publishing against M4, according to https://github.com/scala/scala-java8-compat/blob/master/build.sbt#L13

[szeiger]

I was sure #71 had been merged. Let's try again with a new RC...

[szeiger]

https://github.com/scala/scala-java8-compat/releases/tag/v0.8.0-RC3 published