Do not use sdtin when directories are passed

The check to use stdin was incorrectly true when running with no tty
and no files were passed as arguments, even though directories were
passed with -d

Fixes #184

main.go

@@ -65,7 +65,9 @@ var RootCmd = &cobra.Command{
 		}
 		// We detect whether we have anything on stdin to process if we have no arguments
 		// or if the argument is a -
-		if (len(args) < 1 || args[0] == "-") && !windowsStdinIssue && ((stat.Mode() & os.ModeCharDevice) == 0) {
+		notty := (stat.Mode() & os.ModeCharDevice) == 0
+		noFileOrDirArgs := (len(args) < 1 || args[0] == "-") && len(directories) < 1
+		if noFileOrDirArgs && !windowsStdinIssue && notty {
 			var buffer bytes.Buffer
 			scanner := bufio.NewScanner(os.Stdin)
 			for scanner.Scan() {