Use HTTPS for crossref
@ -127,7 +127,7 @@ engines:
- name : crossref
engine : json_engine
paging : True
search_url : http://search.crossref.org/dois?q={query}&page={pageno}
search_url : https://search.crossref.org/dois?q={query}&page={pageno}
url_query : doi
title_query : title
content_query : fullCitation