main.js.erb in softcover-1.2.11

- old
+ new

@@ -24,9 +24,10 @@
   chapter_number = $('.chapter').attr('data-number')
 
   script = document.createElement( 'script' )
   script.id = 'mathJaxJS'
   script.type = 'text/javascript'
+  script.setAttribute('async', true)
   script.src = '<%= @mathjax_src %>'
   script.innerHTML = """
     <%= @mathjax_config %>
     """
 