Use USTC reverse proxy for Google fonts

layouts/partials/header.html

@@ -80,7 +80,7 @@
 
   {{/* We cannot use SRI with Google Fonts because the CSS is dynamically generated according to the user agent. */}}
   {{ with ($scr.Get "google_fonts") }}
-  <link rel="stylesheet" href="{{ printf "//fonts.googleapis.com/css?family=%s" . }}">
+  <link rel="stylesheet" href="{{ printf "//fonts.proxy.ustclug.org/css?family=%s" . }}">
   {{ end }}
 
   <link rel="stylesheet" href="{{ "styles.css" | relLangURL }}">