Check why Vaccine is breaking in the tests

[luabida]

self = <pysus.tests.test_data.test_vaccine.VaccineTestCase testMethod=test_Download>

    def test_Download(self):
        """Careful! this download can take a long time"""
        df = download_covid("BA", only_header=True)
>       self.assertIsInstance(df, pd.DataFrame)
E       AssertionError: <pandas.io.parsers.readers.TextFileReader object at 0x7ff8eb092ec0> is not an instance of <class 'pandas.core.frame.DataFrame'>

test_data/test_vaccine.py:12: AssertionError