Fix SafeConfigParser deprecation warning in cli
Replace SafeConfigParser with ConfigParser as suggested by the warning.
waiverdb/cli.py:187: DeprecationWarning: The SafeConfigParser class
has been renamed to ConfigParser in Python 3.2. This alias will be
removed in future versions. Use ConfigParser directly instead.
Signed-off-by: Lukas Holecek <hluk@email.cz>