relicense under Apache 2.0

[SethTisue]

just like e.g. scala/scala-xml#242 and scala/scala-parser-combinators#184

[Sciss]

Note that this probably needs a change in defaults: https://github.com/scala/sbt-scala-module/blob/7aee2b537d30f227f2bb27ac6b1c09d5e94dcdf1/src/main/scala/ScalaModulePlugin.scala#L130

[SethTisue]

ah, good catch. I opened scala/sbt-scala-module#48 on it

[SethTisue]

in the meantime, we can

+    // this line could be removed after https://github.com/scala/sbt-scala-module/issues/48 is fixed
+    licenses := Seq(("Apache-2.0", url("https://www.apache.org/licenses/LICENSE-2.0"))),