Windows 10 Fastboot Driver
By looking at the inf file, you can find that it tells to use the WinUSB driver. So there is a better solution than disabling driver signature enforcement, you can use the tool Zadig (http://zadig.akeo.ie/). This tools create a self-signed inf for this specific device, using ephemeral keys, added to the trusted certificate store (for this only device / inf), removing the need to disable signature check.

So you can do this : 


Download the tool, start it.
Select the "S1Boot fastboot" device
Select the WinUSB Driver
Click Install


And then fastboot devices list your device.