Publish for Scala 2.13

[SethTisue]

previous go-round was #68

we don't need to re-test on 2.13.0, so we don't need to wait for ScalaCheck. or we could temporarily use the RC3 artifact

[SethTisue]

• commit 70b5991
• tag https://github.com/scala/scala-parallel-collections/releases/tag/v0.2.0%232.13.0%238
• job https://travis-ci.org/scala/scala-parallel-collections/builds/543175322

[SethTisue]

staging repo closed, released

artifacts to appear here: https://repo1.maven.org/maven2/org/scala-lang/modules/scala-parallel-collections_2.13/0.2.0/