Cannot import debian_oval -> "Failed to get updated_advisories"

Error reported in logs but final message returns "Successfully imported data from debian_oval"

Full logs here:
```
# python manage.py import debian_oval
Importing data from debian_oval
Failed to get updated_advisories: with {'type': 'deb', 'namespace': 'debian', 'qualifiers': {'distro': 'wheezy'}}:
Traceback (most recent call last):
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 481, in updated_advisories
oval_data = self.get_data_from_xml_doc(oval_file, metadata)
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 538, in get_data_from_xml_doc
affected_version_range = VersionSpecifier.from_scheme_version_spec_string(
File "/usr/local/lib/python3.8/site-packages/univers/version_specifier.py", line 137, in from_scheme_version_spec_string
rng = VersionRange(version_range, scheme)
File "/usr/local/lib/python3.8/site-packages/univers/version_range.py", line 42, in __init__
self.version = version_class(self.version)
File "/usr/local/lib/python3.8/site-packages/univers/versions.py", line 152, in __init__
object.__setattr__(self, "value", _DebianVersion.from_string(version_string))
File "/usr/local/lib/python3.8/site-packages/univers/debian.py", line 130, in from_string
raise ValueError('Invalid version string: "{}"'.format(version))
ValueError: Invalid version string: "of"Failed to get updated_advisories: with {'type': 'deb', 'namespace': 'debian', 'qualifiers': {'distro': 'stretch'}}:
Traceback (most recent call last):
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 481, in updated_advisories
oval_data = self.get_data_from_xml_doc(oval_file, metadata)
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 538, in get_data_from_xml_doc
affected_version_range = VersionSpecifier.from_scheme_version_spec_string(
File "/usr/local/lib/python3.8/site-packages/univers/version_specifier.py", line 137, in from_scheme_version_spec_string
rng = VersionRange(version_range, scheme)
File "/usr/local/lib/python3.8/site-packages/univers/version_range.py", line 42, in __init__
self.version = version_class(self.version)
File "/usr/local/lib/python3.8/site-packages/univers/versions.py", line 152, in __init__
object.__setattr__(self, "value", _DebianVersion.from_string(version_string))
File "/usr/local/lib/python3.8/site-packages/univers/debian.py", line 130, in from_string
raise ValueError('Invalid version string: "{}"'.format(version))
ValueError: Invalid version string: "3.8.20-4."Failed to get updated_advisories: with {'type': 'deb', 'namespace': 'debian', 'qualifiers': {'distro': 'jessie'}}:
Traceback (most recent call last):
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 481, in updated_advisories
oval_data = self.get_data_from_xml_doc(oval_file, metadata)
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 538, in get_data_from_xml_doc
affected_version_range = VersionSpecifier.from_scheme_version_spec_string(
File "/usr/local/lib/python3.8/site-packages/univers/version_specifier.py", line 137, in from_scheme_version_spec_string
rng = VersionRange(version_range, scheme)
File "/usr/local/lib/python3.8/site-packages/univers/version_range.py", line 42, in __init__
self.version = version_class(self.version)
File "/usr/local/lib/python3.8/site-packages/univers/versions.py", line 152, in __init__
object.__setattr__(self, "value", _DebianVersion.from_string(version_string))
File "/usr/local/lib/python3.8/site-packages/univers/debian.py", line 130, in from_string
raise ValueError('Invalid version string: "{}"'.format(version))
ValueError: Invalid version string: "initially"Failed to get updated_advisories: with {'type': 'deb', 'namespace': 'debian', 'qualifiers': {'distro': 'buster'}}:
Traceback (most recent call last):
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 481, in updated_advisories
oval_data = self.get_data_from_xml_doc(oval_file, metadata)
File "/opt/vulnerablecode/vulnerabilities/data_source.py", line 538, in get_data_from_xml_doc
affected_version_range = VersionSpecifier.from_scheme_version_spec_string(
File "/usr/local/lib/python3.8/site-packages/univers/version_specifier.py", line 137, in from_scheme_version_spec_string
rng = VersionRange(version_range, scheme)
File "/usr/local/lib/python3.8/site-packages/univers/version_range.py", line 42, in __init__
self.version = version_class(self.version)
File "/usr/local/lib/python3.8/site-packages/univers/versions.py", line 152, in __init__
object.__setattr__(self, "value", _DebianVersion.from_string(version_string))
File "/usr/local/lib/python3.8/site-packages/univers/debian.py", line 130, in from_string
raise ValueError('Invalid version string: "{}"'.format(version))
ValueError: Invalid version string: "3.8.20-4."
Successfully imported data from debian_oval
```