Minor bugfix.

cli/src/main/groovy/com/jdbernard/wdiwtlt/cli/CommandLineInterface.groovy

@@ -90,7 +90,7 @@ Configuration:
         def opts = new Docopt(DOC).withVersion("wdiwtlt v$VERSION").parse(args)
 
         def exitErr = { msg ->
-            System.out.err.println("wdiwtlt: $msg")
+            System.err.println("wdiwtlt: $msg")
             System.exit(1) }
 
         // Look for a given CLI config file.