Update instructions to JINJA_ENVIRONMENT

JINJA_ENVIRONMENT replace JINJA_EXTENSIONS. It was changed in the
example codes but not in the how to localize templates with Jinja2.

localizing_using_jinja2.rst

@@ -6,11 +6,13 @@ Localizing themes with Jinja2
 ---------------------
 
 To enable the |ext| extension in your templates, you must add it to
-``JINJA_EXTENSIONS`` in your Pelican configuration
+``JINJA_ENVIRONMENT`` in your Pelican configuration
 
 .. code-block:: python
 
-  JINJA_EXTENSIONS = ['jinja2.ext.i18n', ...]
+  JINJA_ENVIRONMENT = {
+    'extensions': ['jinja2.ext.i18n', ...]
+  }
 
 Then follow the `Jinja2 templating documentation for the I18N plugin
 <http://jinja.pocoo.org/docs/templates/#i18n>`_ to make your templates