typo

src/modbus-rtu.c

@@ -353,7 +353,7 @@ static int _modbus_rtu_pre_check_confirmation(modbus_t *ctx, const uint8_t *req,
     }
 }
 
-/* The check_crc16 function shall return 0 is the message is ignored and the
+/* The check_crc16 function shall return 0 if the message is ignored and the
    message length if the CRC is valid. Otherwise it shall return -1 and set
    errno to EMBBADCRC. */
 static int _modbus_rtu_check_integrity(modbus_t *ctx, uint8_t *msg,