Update sbt-ci-release to 1.8.0 (#886)

Author: scala-steward

project/plugins.sbt

@@ -1,6 +1,6 @@
 resolvers += Classpaths.sbtPluginReleases
 
-addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.7.0")
+addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.8.0")
 addSbtPlugin("com.eed3si9n"   % "sbt-assembly"   % "0.14.10")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"   % "2.5.2")
 addSbtPlugin("org.scoverage"  % "sbt-scoverage"  % "2.2.1")