Update README.md

the wrong refresh route in the document [remove the end slash]

README.md

@@ -116,7 +116,7 @@ curl \
   -X POST \
   -H "Content-Type: application/json" \
   -d '{"refresh":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX3BrIjoxLCJ0b2tlbl90eXBlIjoicmVmcmVzaCIsImNvbGRfc3R1ZmYiOiLimIMiLCJleHAiOjIzNDU2NywianRpIjoiZGUxMmY0ZTY3MDY4NDI3ODg5ZjE1YWMyNzcwZGEwNTEifQ.aEoAYkSJjoWH1boshQAaTkf8G3yn0kapko6HFRt7Rh4"}' \
-  http://localhost:8000/api/token/refresh/
+  http://localhost:8000/api/token/refresh
 
 ...
 {"access":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX3BrIjoxLCJ0b2tlbl90eXBlIjoiYWNjZXNzIiwiY29sZF9zdHVmZiI6IuKYgyIsImV4cCI6MTIzNTY3LCJqdGkiOiJjNzE4ZTVkNjgzZWQ0NTQyYTU0NWJkM2VmMGI0ZGQ0ZSJ9.ekxRxgb9OKmHkfy-zs1Ro_xs1eMLXiR17dIDBVxeT-w"}