I checked the product page in this link: IO Expansion Shield for Intel® Edison (without Edison), and it seems that other users have asked the same question before.
You should check the schematic of this expansion board (https://github.com/Arduinolibrary/DFRobot_IO_expansion_board_for_Edison/blob/master/IO%20expansion%20board%20for%20Ediso…) and the following MRAA table: mraa: Intel Edison. The table shows how the physical pins are mapped to the MRAA pin numbers. The pin 13, for example, is connected to the GP40 of the Edison module which is mapped to the MRAA number 37. This means that you should use the number 37 in your code instead of the number 13.