Traceback - exit whitout action

```
$ python3 --version
Python 3.5.3
```

```
$ ./temper.py --help
Traceback (most recent call last):
  File "./temper.py", line 410, in <module>
    temper = Temper()
  File "./temper.py", line 258, in __init__
    self.usb_devices = usblist.get_usb_devices()
  File "./temper.py", line 99, in get_usb_devices
    with os.scandir(Temper.SYSPATH) as it:
AttributeError: __exit__
```