Fix #3606: MathJax should be loaded with async attribute

CHANGES

@@ -117,6 +117,7 @@ Features added
 * #4785: napoleon: Add strings to translation file for localisation
 * #4927: Display a warning when invalid values are passed to linenothreshold
   option of highlight directive
+* #3606: MathJax should be loaded with async attribute
 
 Bugs fixed
 ----------

sphinx/ext/mathjax.py

@@ -72,7 +72,8 @@ def builder_inited(app):
     if not app.config.mathjax_path:
         raise ExtensionError('mathjax_path config value must be set for the '
                              'mathjax extension to work')
-    app.add_js_file(app.config.mathjax_path)
+    options = {'async': 'async'}
+    app.add_js_file(app.config.mathjax_path, **options)
 
 
 def setup(app):