Update sbt-ci-release to 1.6.0 (#386)

Author: scala-steward

project/plugins.sbt

@@ -8,7 +8,7 @@ val scalaNativeVersion = "0.5.4"
 val scalafix = "0.12.1"
 
 // includes sbt-dynver sbt-pgp sbt-sonatype sbt-git
-addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.12")
+addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.6.0")
 addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "1.1.4")
 
 // Scala Native support