Update sbt-scalafix to 0.9.18

Author: scala-steward

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("io.github.davidgregory084" % "sbt-tpolecat" % "0.1.13")
-addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.17")
+addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.18")
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.4.0")
 addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.3")
 addSbtPlugin("com.47deg" % "sbt-microsites" % "1.2.1")