Merge pull request #214 from scala-steward/update/sbt-scalafmt-2.5.5

Update sbt-scalafmt to 2.5.5

Author: mkurz

project/plugins.sbt

@@ -1,4 +1,4 @@
 // The Play plugin
 addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.9.7")
 
-addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.2")
+addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.5")