Update sbt-ci-release to 1.5.6 (#124)

Author: scala-steward

build.sbt

@@ -11,4 +11,4 @@ addSbtPlugin("com.typesafe.sbt" % "sbt-osgi" % "0.9.6")
 addSbtPlugin("de.heikoseeberger" % "sbt-header" % "5.6.0")
 addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.8.1")
 addSbtPlugin("com.dwijnand" % "sbt-travisci" % "1.2.0")   // set scalaVersion and crossScalaVersions
-addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.5") // set version, scmInfo, publishing settings
+addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.6") // set version, scmInfo, publishing settings

project/plugins.sbt

@@ -1 +1 @@
-addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.5")
+addSbtPlugin("com.geirsson" % "sbt-ci-release" % "1.5.6")