Update sbt-typelevel, sbt-typelevel-site to 0.4.20

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -2,6 +2,6 @@ addSbtPlugin("org.scala-js"       % "sbt-scalajs"                   % "1.13.1")
 addSbtPlugin("org.scala-native"   % "sbt-scala-native"              % "0.4.12")
 addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.3.1")
 addSbtPlugin("pl.project13.scala" % "sbt-jmh"                       % "0.4.4")
-val sbtTypelevelVersion = "0.4.19"
+val sbtTypelevelVersion = "0.4.20"
 addSbtPlugin("org.typelevel" % "sbt-typelevel"      % sbtTypelevelVersion)
 addSbtPlugin("org.typelevel" % "sbt-typelevel-site" % sbtTypelevelVersion)