Fixed type attribute key error.

[GRMrGecko]

Traceback (most recent call last):
File "/usr/bin/backup-vm", line 11, in
load_entry_point('backup-vm==0.1.dev28+g442ce38', 'console_scripts', 'backup-vm')() File "/usr/lib/python3.8/site-packages/backup_vm-0.1.dev28+g442ce38-py3.8.egg/backup_vm/backup.py", line 24, in main
all_disks = set(parse.Disk.get_disks(dom))
File "/usr/lib/python3.8/site-packages/backup_vm-0.1.dev28+g442ce38-py3.8.egg/backup_vm/parse.py", line 196, in get_disks
yield from {d for d in map(cls, tree.findall("devices/disk")) if d.type is not None}
File "/usr/lib/python3.8/site-packages/backup_vm-0.1.dev28+g442ce38-py3.8.egg/backup_vm/parse.py", line 196, in
yield from {d for d in map(cls, tree.findall("devices/disk")) if d.type is not None}
File "/usr/lib/python3.8/site-packages/backup_vm-0.1.dev28+g442ce38-py3.8.egg/backup_vm/parse.py", line 171, in init
self.format = xml.find("driver").attrib["type"]
KeyError: 'type'

[milkey-mouse]

Thanks!