Update README for new reference of line numbers

Error codes and return codes were referenced incorrectly (probably due to changes in the referenced file). I have updated those to refer to the correct line numbers.

README.md

@@ -243,8 +243,8 @@ lwmqtt_err_t lastError();
 lwmqtt_return_code_t returnCode();
 ```
 
-- The error codes can be found [here](https://github.com/256dpi/lwmqtt/blob/master/include/lwmqtt.h#L11).
-- The return codes can be found [here](https://github.com/256dpi/lwmqtt/blob/master/include/lwmqtt.h#L243).
+- The error codes can be found [here](https://github.com/256dpi/lwmqtt/blob/master/include/lwmqtt.h#L15).
+- The return codes can be found [here](https://github.com/256dpi/lwmqtt/blob/master/include/lwmqtt.h#L260).
 
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