yml_utils.py: inconsistent use of tabs and spaces in indentation

[garvankeeley]

y$ /usr/local/bin/python3 ./ios_advisories.py 
Traceback (most recent call last):
  File "./ios_advisories.py", line 17, in <module>
    from yml_utils import *
  File "/Users/gkeeley/code/foo/secadv/yml_utils.py", line 44
    name = re.sub(" \(ni [^\)]+\)", "", name)
                                            ^
TabError: inconsistent use of tabs and spaces in indentation