Update build plugin

Author: adamw

project/plugins.sbt

@@ -3,7 +3,7 @@ addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.3.1")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.4.0-M2")
 addSbtPlugin("com.eed3si9n" % "sbt-projectmatrix" % "0.6.0")
 
-val sbtSoftwareMillVersion = "1.9.15-SNAPSHOT"
+val sbtSoftwareMillVersion = "1.9.15"
 addSbtPlugin("com.softwaremill.sbt-softwaremill" % "sbt-softwaremill-common" % sbtSoftwareMillVersion)
 addSbtPlugin("com.softwaremill.sbt-softwaremill" % "sbt-softwaremill-publish" % sbtSoftwareMillVersion)
 addSbtPlugin("com.softwaremill.sbt-softwaremill" % "sbt-softwaremill-browser-test-js" % sbtSoftwareMillVersion)