clarify intent

ivy/src/main/scala/sbt/internal/librarymanagement/ivyint/ParallelResolveEngine.scala

@@ -38,6 +38,7 @@ private[sbt] class ParallelResolveEngine(settings: ResolveEngineSettings,
     val allDownloads = dependencies.par.flatMap { dep =>
       if (!(dep.isCompletelyEvicted || dep.hasProblem) &&
           dep.getModuleRevision != null) {
+        //don't block in global ec to avoid deadlocks
         scala.concurrent.blocking {
           ParArray(downloadNodeArtifacts(dep, artifactFilter, options))
         }