still a bug in doc generation

tools/travis_push_doc.sh

@@ -4,6 +4,7 @@ git clone --depth=5 -b gh-pages https://$GITAUTH@github.com/open62541/open62541-
 cd open62541-www
 
 git rm -r -f ./doc/current/*
+mkdir ./doc/current
 cp -r ../../doc/* ./doc/current/
 git add -A ./doc/current
 git config --global user.email "open62541-travis-ci@users.noreply.github.com"