Backpublish 1.0.0 for Scala 3.0.0-M2

[SethTisue]

• wait for ScalaCheck to publish
  • Publish for Scala 3.0.0-M2, please typelevel/scalacheck#723
  • note that if needed we could also just withDottyCompat it in the backpublish commit, but meh
• replace M1 with M2 in the crossbuild
  • bump Scala versions (to 2.13.4 and 3.0.0-M2) #144
• choose version number
  • let's just backpublish 1.0.0, I see no need to bump the version
• push the tag
  • https://github.com/scala/scala-parallel-collections/releases/tag/v1.0.0%233.0.0-M2 (not on any branch)
• wait for release build
  • https://travis-ci.com/github/scala/scala-parallel-collections/builds/204322591
• release the staging repo
• artifacts on Maven Central
  • https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parallel-collections_3.0.0-M2/1.0.0/