fix sitemap location

Author: kinkie

doxyfile

@@ -1613,7 +1613,7 @@ TOC_EXPAND             = NO
 # protocol see https://www.sitemaps.org
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-SITEMAP_URL            = /sitemap.xml
+SITEMAP_URL            = https://code-reference.squid-cache.org
 
 # If the GENERATE_QHP tag is set to YES and both QHP_NAMESPACE and
 # QHP_VIRTUAL_FOLDER are set, an additional index file will be generated that