aws-saml fails when missing SESSION_DURATION

[zaro0508]

The --session-duration parameter should be an optional argument however aws-saml fails when it's not set.

➜ python -V
Python 3.7.7

➜ pip freeze
awscli-saml==2.0.0
boto3==1.13.16
botocore==1.16.16
docutils==0.15.2
jmespath==0.10.0
python-dateutil==2.8.1
s3transfer==0.3.3
six==1.15.0
urllib3==1.25.9

➜ aws-saml --profile central-admin  \
         --idp-arn arn:aws:iam::111111111111:saml-provider/central-admin \
         --role-arn arn:aws:iam::111111111111:role/central-admin
Traceback (most recent call last):
  File "/Users/zaro0508/.virtualenvs/py37-test2/bin/aws-saml", line 8, in <module>
    sys.exit(main())
  File "/Users/zaro0508/.virtualenvs/py37-test2/lib/python3.7/site-packages/awscli_saml/main.py", line 44, in main
    saml=args.saml,
  File "/Users/zaro0508/.virtualenvs/py37-test2/lib/python3.7/site-packages/awscli_saml/assume_role.py", line 28, in run
    section_name, "saml.session_duration"
  File "/usr/local/var/pyenv/versions/3.7.7/lib/python3.7/configparser.py", line 818, in getint
    fallback=fallback, **kwargs)
  File "/usr/local/var/pyenv/versions/3.7.7/lib/python3.7/configparser.py", line 808, in _get_conv
    **kwargs)
  File "/usr/local/var/pyenv/versions/3.7.7/lib/python3.7/configparser.py", line 802, in _get
    return conv(self.get(section, option, **kwargs))
  File "/usr/local/var/pyenv/versions/3.7.7/lib/python3.7/configparser.py", line 780, in get
    d = self._unify_values(section, vars)
  File "/usr/local/var/pyenv/versions/3.7.7/lib/python3.7/configparser.py", line 1146, in _unify_values
    raise NoSectionError(section) from None
configparser.NoSectionError: No section: 'profile central-admin'