Update nscplugin, sbt-scala-native, ... to 0.4.15 (#576)

Author: scala-steward

project/plugins.sbt

@@ -1,7 +1,7 @@
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.13.2")
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-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.portable-scala" % "sbt-scala-native-crossproject" % "1.3.2")
 
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.12")