Revert "Update sbt-scalafix, scalafix-core to 0.12.0 (#499)"

This reverts commit ef4b13cc0b53ed8c99730fd63928e61de6a836b8.
diff --git a/project/plugins.sbt b/project/plugins.sbt
index 6bbd6f1..4622e56 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -27,7 +27,7 @@
 
 addSbtPlugin("de.heikoseeberger" % "sbt-header" % "5.10.0")
 addSbtPlugin("net.bzzt" % "sbt-reproducible-builds" % "0.32")
-addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.12.0")
+addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.11.1")
 addSbtPlugin("com.github.sbt" % "sbt-dynver" % "5.0.1")
 addSbtPlugin("com.github.pjfanning" % "sbt-source-dist" % "0.1.12")
 addSbtPlugin("com.github.pjfanning" % "sbt-pekko-build" % "0.3.3")