Workaround for scalaBinaryVersion handling for 2.12.x

This will be rolled into sbt-scala-modules soon, but I'd
like to get the ball rolling here.

Author: retronym

build.sbt

@@ -12,9 +12,18 @@ scalaXmlVersion            := "1.0.1"
 
 scalaCheckVersion          := "1.11.3"
 
-// used as binary version when compiling against 2.11.0-SNAPSHOT
+// used as binary version when compiling against 2.12.0-SNAPSHOT
 snapshotScalaBinaryVersion := "2.11.0"
 
+// TODO remove this after https://github.com/scala/sbt-scala-modules/pull/7
+//      is merged and this build refers to the new plugin.
+scalaBinaryVersion := (
+  if (scalaVersion.value.startsWith("2.12"))
+    snapshotScalaBinaryVersion.value
+  else
+    scalaBinaryVersion.value
+)
+
 // TODO: enable "-Xfatal-warnings" for nightlies,
 // off by default because we don't want to break scala/scala pr validation due to deprecation
 // don't use for doc scope, scaladoc warnings are not to be reckoned with