Added -Ypartial-unification to scalac options

See scala/bug#2712

Author: nloyola

build.sbt

@@ -161,6 +161,7 @@ scalacOptions ++=
       "-language:postfixOps",
       "-unchecked", // additional warnings where generated code depends on assumptions
       "-Xlint:_",
+      "-Ypartial-unification",
       "-Ywarn-adapted-args", // Warn if an argument list is modified to match the receiver
       "-Ywarn-dead-code",
       "-Ywarn-inaccessible",