Update nscplugin, sbt-scala-native, ... to 0.4.15 (#533)

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.3.2")
-addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.4.14")
+addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.4.15")
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.13.2")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.0.9")
 addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.6")