Fix compiler error with refined 0.7

The error was "Class scala.tools.nsc.Global not found - continuing with
a stub.", and the fix is to add a provided dep on the scala compiler.

See fthomas/refined#256 for details.

build.sbt

@@ -63,6 +63,10 @@ lazy val root = (project in file("."))
     // Dependencies
     libraryDependencies ++= Seq(
       "com.typesafe.play" %% "play-json" % "2.5.0",
+      // Fix "Class scala.tools.nsc.Global not found - continuing with a stub."
+      // build failure by adding a provided dep on the scala-compiler, see
+      // https://github.com/fthomas/refined/issues/256
+      "org.scala-lang" % "scala-compiler" % scalaVersion.value % Provided,
       "eu.timepit" %% "refined" % "0.7.0",
       "org.scalacheck" %% "scalacheck" % "1.13.4" % "test"
     ),