FutureWarnings in epidata code

[patricklnz]

The following FutureWarnings occurred:
In getCaseData lines 662, 719 when executing the coresponding test:
FutureWarning: Passing literal json to 'read_json' is deprecated and will be removed in a future version. To read from a literal string, wrap it in a 'StringIO' object.
In getVaccinationData line 146:
FutureWarning: Setting an item of incompatible dtype is deprecated and will raise an error in a future version of pandas.
In getVaccinationData line 520:
FutureWarning: Series.__getitem__ treating keys as positions is deprecated.
In getNPIData line 926:
FutureWarning: Downcasting behavior in 'replace' is deprecated and will be removed in a future version.