Update sbt-header to 5.4.0 (#78)

Author: scala-steward

build.sbt

@@ -5,7 +5,7 @@ organization        := "org.scala-lang.modules"
 licenses            := Seq(("Apache-2.0", url("https://www.apache.org/licenses/LICENSE-2.0")))
 
 addSbtPlugin("com.typesafe.sbt" % "sbt-osgi" % "0.9.5")
-addSbtPlugin("de.heikoseeberger" % "sbt-header" % "5.3.1")
+addSbtPlugin("de.heikoseeberger" % "sbt-header" % "5.4.0")
 addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.6.1")
 addSbtPlugin("com.dwijnand" % "sbt-travisci" % "1.2.0")   // set scalaVersion and crossScalaVersions
 addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.0") // set version, scmInfo, publishing settings