example code correction

README.md

@@ -22,7 +22,7 @@ api = LimeSurvey(url=url, username=username)
 api.open(password=password)
 
 # Get a list of surveys the admin can see, and print their IDs.
-result = self.api.survey.list_surveys()
+result = api.survey.list_surveys()
 for survey in result:
     print(survey.get("sid"))