Improve Zipper to support root directory and fix bug in root directory normalization

Change-Id: I7f00a347fb4616cb8ae7df63374633c21d7ab0ce
diff --git a/t/tokenization.t b/t/tokenization.t
index 9fbf4d1..8a1aba6 100644
--- a/t/tokenization.t
+++ b/t/tokenization.t
@@ -132,7 +132,7 @@
 subtest 'Test Zipper' => sub {
   # Test Zipper
   my ($fh, $outzip) = korap_tempfile('tokenize_zipper');
-  my $zip = KorAP::XML::TEI::Zipper->new($outzip);
+  my $zip = KorAP::XML::TEI::Zipper->new('', $outzip);
   $fh->close;
 
   my $aggr = KorAP::XML::TEI::Tokenizer::Aggressive->new;