fixing typo in docs, piccolo_conf -> piccolo_app

Thanks Matthieu!

Author: dantownsend

docs/src/piccolo/authentication/index.rst

@@ -10,7 +10,7 @@ Piccolo ships with some authentication support out of the box.
 Registering the app
 -------------------
 
-Make sure ``'piccolo.apps.user.piccolo_conf'`` is in your ``AppRegistry`` (see
+Make sure ``'piccolo.apps.user.piccolo_app'`` is in your ``AppRegistry`` (see
 :ref:`PiccoloProjects`).
 
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