Fixed minor bug in contributing documentation

Signed-off-by: Brian Rosner <brosner@gmail.com>

docs/contributing.txt

@@ -53,7 +53,7 @@ from within the clone (the ``pinax`` directory)::
 If you use virtualenvwrapper you could alternatively do::
 
     python scripts/pinax-boot.py --development --source=. $WORKON_HOME/pinax-dev
-    workon pinax-development
+    workon pinax-dev
 
 Finally, you need to install the dependencies for the development version::