How about this:
```scala
    libraryDependencies ++= {
      CrossVersion.partialVersion(scalaVersion.value) match {
        case Some((2, scalaMajor)) if scalaMajor >= 11 =>
          Seq(
            "org.scala-lang.modules" %% "scala-parser-combinators" % "1.0.1"
          )
        case _ => Seq.empty
      }
    }
```
Using `scalaVersion.value` in `~=` seems to be forbidden:
```
[info] Compiling 1 Scala source to /Users/georgii/workspace/util/project/target/scala-2.10/sbt-0.13/classes...
[error] /Users/georgii/workspace/util/project/Build.scala:33: `value` can only be used within a task or setting macro, such as :=, +=, ++=, Def.task, or Def.setting.
[error]       dependencies ++ (CrossVersion.partialVersion(scalaVersion.value) match {
[error]                                                                 ^
[error] one error found
[error] (compile:compile) Compilation failed
```