Update head.html

"Bad value http://fonts.googleapis.com/css?family=PT+Serif:400,400italic,700|PT+Sans:400 for attribute href on element link: Illegal character in query: not a URL code point." Source: http://validator.w3.org

Solution explained here: http://stackoverflow.com/questions/22466913/google-fonts-url-break-html5-validation-on-w3-org