Fix small typo  [ci skip]
@@ -721,7 +721,7 @@ class AjaxDataSource(RemoteSource):
format.
If provided, this callback is executes immediately after the JSON data is
- received, but before apprending or replacing data in the data source. The
+ received, but before appending or replacing data in the data source. The
CustomJS callback will receive the AjaxDataSource as ``cb_obj`` and will
receive the raw JSON response as ``cb_data.response``. The callback code
should return a ``data`` object suitable for a Bokeh ColumnDataSource (i.e.
