Upgrade sbt-coursier plugin

Author: xerial

project/plugin.sbt

@@ -1,7 +1,7 @@
 addSbtPlugin("com.github.gseitz" % "sbt-release" % "1.0.3")
 addSbtPlugin("org.xerial.sbt" % "sbt-sonatype" % "1.1")
 addSbtPlugin("com.jsuereth" % "sbt-pgp" % "1.0.0")
-addSbtPlugin("io.get-coursier" % "sbt-coursier" % "1.0.0-M14-7")
+addSbtPlugin("io.get-coursier" % "sbt-coursier" % "1.0.0-M15")
 addSbtPlugin("net.virtual-void" % "sbt-dependency-graph" % "0.7.5")
 
 scalacOptions ++= Seq("-deprecation", "-feature")