Update sbt-scalajs, scalajs-library_2.13, ... to 1.20.1 (#450)

Author: scala-steward

project/plugins.sbt

@@ -2,7 +2,7 @@ addSbtPlugin("org.scalameta"      % "sbt-scalafmt"             % "2.5.5")
 addSbtPlugin("org.scalastyle"    %% "scalastyle-sbt-plugin"    % "1.0.0")
 addSbtPlugin("org.scoverage"      % "sbt-scoverage"            % "2.3.1")
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "1.3.2")
-addSbtPlugin("org.scala-js"       % "sbt-scalajs"              % "1.19.0")
+addSbtPlugin("org.scala-js"       % "sbt-scalajs"              % "1.20.1")
 addSbtPlugin("com.github.sbt"     % "sbt-ci-release"           % "1.11.2")
 
 // workaround for conflict between sbt-scoverage and scalastyle-sbt-plugin