Fix in keyfetch for obok on win10

According to calibre debug the ipconfig command returned some invalid utf-8 characters (I think is maybe an issue due to the Python2 switch-off as the 4.x version worked fine).
To solve this I've changed the external call and modified the regex to match both the output of "ipconfig" and that of "wmic".

Obok_plugin/obok/obok.py

@@ -470,8 +470,8 @@ class KoboLibrary(object):
         """The list of all MAC addresses on this machine."""
         macaddrs = []
         if sys.platform.startswith('win'):
-            c = re.compile('\s(' + '[0-9a-f]{2}-' * 5 + '[0-9a-f]{2})(\s|$)', re.IGNORECASE)
-            output = subprocess.Popen('ipconfig /all', shell=True, stdout=subprocess.PIPE, text=True).stdout
+            c = re.compile('\s?(' + '[0-9a-f]{2}[:\-]' * 5 + '[0-9a-f]{2})(\s|$)', re.IGNORECASE)
+            output = subprocess.Popen('wmic nic where PhysicalAdapter=True get MACAddress', shell=True, stdout=subprocess.PIPE, text=True).stdout
             for line in output:
                 m = c.search(line)
                 if m: