Docs: fixed some bad example code mixing str % formatting and str.format().

docs/tutorial/steps-from-step-definitions.rst

@@ -43,7 +43,7 @@ Lettuce affords you the ability to write such a "step of steps" with a set of he
 running blocks of steps
 -----------------------
 
-It is sometimes even desirable to run blocks of steps, copy-and-pasted directly from Feature specifications. The ``Step.behave_as`` method lets you do this, and you can use ``string.format`` to fill in parameters dynamically. For example, we can write the above step definition like so:
+It is sometimes even desirable to run blocks of steps, copy-and-pasted directly from Feature specifications. The ``Step.behave_as`` method lets you do this, and you can use ``str.format`` to fill in parameters dynamically. For example, we can write the above step definition like so:
 
 .. highlight:: python
 
@@ -54,11 +54,8 @@ It is sometimes even desirable to run blocks of steps, copy-and-pasted directly
         step.behave_as("""
             Given I go to the home page
               And I click the login button
-              And I fill in username:%(user)s password:%(pass)s
+              And I fill in username:{user} password:{pass}
               And I click "Login"
-        """.format({
-            'user': 'floppy',
-            'pass': 'banana'
-        }))
+        """.format(user='floppy', pass='banana'))
 
 This can be combined with step argument capture for step definitions that are both expressive and DRY.