Update sbt-ci-release to 1.9.3 (lightbend-labs#466)

Author: scala-steward

project/plugins.sbt

@@ -1,3 +1,3 @@
 addSbtPlugin("org.scalariform" % "sbt-scalariform" % "1.8.3")
 addSbtPlugin("com.github.sbt" % "sbt-osgi" % "0.10.0")
-addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.9.2")
+addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.9.3")