go-tour: remove protocol from webfont script tag

Fixes font loading on HTTPS sites.

TBR=dsymonds
R=golang-codereviews
CC=golang-codereviews
https://golang.org/cl/82920043
diff --git a/template/index.tmpl b/template/index.tmpl
index 4f3c3cc..9b497b0 100755
--- a/template/index.tmpl
+++ b/template/index.tmpl
@@ -10,7 +10,7 @@
     <link rel="shortcut icon" sizes="196x196" href="/static/img/favicon.ico">
     <link rel="stylesheet" href="/static/css/app.css" />
     <link rel="stylesheet" href="/static/lib/codemirror/lib/codemirror.css">
-    <link href='http://fonts.googleapis.com/css?family=Inconsolata' rel='stylesheet' type='text/css'>
+    <link href='//fonts.googleapis.com/css?family=Inconsolata' rel='stylesheet' type='text/css'>
 </head>
 
 <body>