Update .htaccess

Set Access-Control-Allow-Origin, don't add to it, which conflicts with that set in /.

Author: gkellogg

contexts/.htaccess

@@ -1,7 +1,7 @@
 <FilesMatch "(event|person|place|recipe|\.jsonld)$">
    ForceType application/ld+json
    SetHandler default_handler
-   Header add Access-Control-Allow-Origin *
+   Header set Access-Control-Allow-Origin *
 </FilesMatch>
 
 Redirect 301 /contexts/schema.org.jsonld http://schema.org/