correcting content_type

:js to :json

Author: ewmanthei

_includes/sinatra-json.html

@@ -78,7 +78,7 @@ <h3 id="label-Content-Type">Content-Type</h3>
 usual, you can easily change that, with the <code>:json_content_type</code>
 setting:</p>
 
-<pre>set :json_content_type, :js</pre>
+<pre>set :json_content_type, :json</pre>
 
 <h3 id="label-Overriding+the+Encoder+and+the+Content-Type">Overriding the Encoder and the Content-Type</h3>