Update sbt-scalafix to 0.13.0 (#216)

Author: scala-steward

project/plugin.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"   % "2.5.2")
-addSbtPlugin("ch.epfl.scala"  % "sbt-scalafix"   % "0.12.1")
+addSbtPlugin("ch.epfl.scala"  % "sbt-scalafix"   % "0.13.0")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.6.1")
 addSbtPlugin("org.scalameta"  % "sbt-mdoc"       % "2.6.1")
 addSbtPlugin("com.github.sbt" % "sbt-unidoc"     % "0.5.0")