The gamecon driver is hosted by the developer Marqs. Maybe he is restructuring it or something.
If you have the RetroPie GPIO Adapter I would suggest to use SNESDev (and only SNESDev, so that it does not interfere with the gamecon driver). You can use the RetroPie Script to enable and configure SNESDev from within the “Setup” menu. See also the thread at https://www.petrockblock.com/forums/topic/snes-gpio-setup-help/.