Fix a Liquid-error

Fix for error 'no implicit conversion of Integer into String'.
Also see: jekyll/jekyll#6319

_includes/head.html

@@ -3,7 +3,7 @@
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1">
 
-  <title>{% if page.title %}{{ page.title | escape }}{% else %}{{ site.title | escape }}{% endif %}</title>
+  <title>{% if page.title %}{{ page.title | escape_once }}{% else %}{{ site.title | escape_once }}{% endif %}</title>
   <meta name="description" content="{% if page.excerpt %}{{ page.excerpt | strip_html | strip_newlines | truncate: 160 }}{% else %}{{ site.description }}{% endif %}">
   <link href='https://fonts.googleapis.com/css?family=PT+Sans:400,700,400italic,700italic|Source+Sans+Pro:400,700,200,300|Josefin+Sans:400,600,700,300' rel='stylesheet' type='text/css'>
   <link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css" rel="stylesheet">