Fix quotes showing in tab title (#26)

A user showed that the tab title showed a `"..."`, this is a bug in Xranklin it seems  due to a difference in `{{fill title}}` vs `{{title}}` (which shouldn't be there). 

tlienart/Xranklin.jl#194

in the meantime this commit should remove those spurious `"`.

Author: tlienart

_layout/head.html

@@ -13,7 +13,7 @@
   {{if hascode}} {{insert head_highlight.html }}   {{end}}
   <script defer data-domain="juliaparallel.org" src="https://plausible.io/js/plausible.js"></script>
   {{insert style.html}}
-  {{isdef title}} <title>{{fill title}}</title>  {{end}}
+  {{isdef title}} <title>{{title}}</title>  {{end}}
   <!-- end custom head snippets -->
 
 </head>