Use valid github username (#1287)

README.rst

@@ -153,8 +153,8 @@ English sentences used within ``misago.faker.phrases`` were extracted from `Nati
 Copyright and license
 =====================
 
-**Misago** - Copyright © 2018 `Rafał Pitoń <http://github.com/ralfp>`_
+**Misago** - Copyright © 2018 `Rafał Pitoń <http://github.com/rafalp>`_
 This program comes with ABSOLUTELY NO WARRANTY.
 
 This is free software and you are welcome to modify and redistribute it under the conditions described in the license.
-For the complete license, refer to LICENSE.rst
+For the complete license, refer to LICENSE.rst