Merge pull request #347 from scala-steward/update/2.3.x/sbt-ci-release-1.9.0

[2.3.x] sbt-ci-release 1.9.0 (was 1.8.0)

Author: mkurz

project/plugins.sbt

@@ -2,4 +2,4 @@ addSbtPlugin("com.typesafe"      % "sbt-mima-plugin"    % "1.1.4")
 addSbtPlugin("com.lightbend.sbt" % "sbt-java-formatter" % "0.8.0")
 addSbtPlugin("de.heikoseeberger" % "sbt-header"         % "5.10.0")
 addSbtPlugin("org.scalameta"     % "sbt-scalafmt"       % "2.5.2")
-addSbtPlugin("com.github.sbt"    % "sbt-ci-release"     % "1.8.0")
+addSbtPlugin("com.github.sbt"    % "sbt-ci-release"     % "1.9.0")