Broken core font links

With this plugin I’m seeing a file that should reference the google fonts api url (https://fonts.googleapis.com/css?family=Open+Sans%3A300italic%2C400italic%2C600italic%2C300%2C400%2C600&subset=latin%2Clatin-ext&ver=4.1.2) being attempted to load via a relative path (http://localhost/css?family=Open+Sans%3A300italic%2C400italic%2C600italic%2C300%2C400%2C600&subset=latin%2Clatin-ext&ver=4.1.2)

Any suggestions?

https://wordpress.org/plugins/relative-url/