Driver doesn't appear for selected shape keys

I"m following a tutorial here: http://cgcookie.com/blender/lessons/6-rigging-the-turtle/ I’m at the part where I am supposed to add drivers for the shape keys to be controlled by the corresponding bones. I right click on the number next to the shape key name and select “add driver” from the menu. It turns pink like in the tutorial. But when I go to the graph editor and change the context to “drivers”, I don’t see the key in the left hand column as in the tutorial. Can someone tell me what I am doing wrong?

Blend file: http://www.pasteall.org/blend/25985

From the tutorial:
http://i846.photobucket.com/albums/ab27/blanco1111/help11_zps58846c91.png

What I get:
http://i846.photobucket.com/albums/ab27/blanco1111/help10_zps8295631b.png

Try scrolling up in the graph editor window.



Thank you.