Fix createDate to be creationDate

Change-Id: I382a2f450c86dec506413c7245630e5323e7b487
diff --git a/lib/KorAP/VirtualCorpus/Group.pm b/lib/KorAP/VirtualCorpus/Group.pm
index 8e77fff..e7dd8d4 100644
--- a/lib/KorAP/VirtualCorpus/Group.pm
+++ b/lib/KorAP/VirtualCorpus/Group.pm
@@ -149,7 +149,7 @@
 sub from {
   my $self = shift;
   my ($year, $month) = @_;
-  my $doc = KorAP::VirtualCorpus::Doc->new('createDate')
+  my $doc = KorAP::VirtualCorpus::Doc->new('creationDate')
     ->type('date')
     ->match('geq')
     ->value($year . '-' . $month);
@@ -161,7 +161,7 @@
 sub to {
   my $self = shift;
   my ($year, $month) = @_;
-  my $doc = KorAP::VirtualCorpus::Doc->new('createDate')
+  my $doc = KorAP::VirtualCorpus::Doc->new('creationDate')
     ->type('date')
     ->match('leq')
     ->value($year . '-' . $month);