Correct spelling in documentation.

Author: senotrusov

docs/_includes/options/data/selection-access.html

@@ -38,7 +38,7 @@ <h2 id="selection-api-access">
 {% endhighlight %}
 
   <p>
-    In addition, properties/values from source data objects can ba accessed from within event handler:
+    In addition, properties/values from source data objects can ba accessed from within an event handler:
   </p>
 
 {% highlight js linenos %}