Update sbt-scalajs, scalajs-library, ... to 1.6.0 (#237)

Author: scala-steward

project/plugins.sbt

@@ -2,7 +2,7 @@ addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "1.0.0")
 addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.10.0")
 addSbtPlugin("com.lightbend.paradox" % "sbt-paradox" % "0.9.2")
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "1.0.0")
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.5.1")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.6.0")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "1.8.2")
 addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.3")
 addSbtPlugin("com.codecommit" % "sbt-spiewak-sonatype" % "0.21.0")