fix: ignore a return code in travis documentation generation

tools/travis/travis_push_doc.sh

@@ -4,7 +4,7 @@ set -ev
 git clone --depth=5 -b gh-pages https://$GITAUTH@github.com/open62541/open62541-www
 cd open62541-www
 
-git rm -r -f ./doc/current/*
+rm -r -f ./doc/current/* || true # ignore result
 mkdir ./doc/current
 cp -r ../../doc/* ./doc/current/
 git add -A ./doc/current
@@ -13,4 +13,5 @@ git config --global user.name "Open62541 travis-ci"
 git config --global push.default simple
 git commit -am "updated generated documentation on webpage by travis-ci [ci skip]"
 git push https://$GITAUTH@github.com/open62541/open62541-www
+
 cd .. && rm -rf open62541-www