replacing get_record with get_dv

[jmframe]

Somehow the get_record wasn't working for the time series. replaced it with get_dv. Don't know why that is needed, but worth looking into.

[jmframe]

This addresses issue #9

[sumabattula]

This still gave missing value. But then when I used get_dv without specifying service, startDT, and endDT options, it worked.

df, _ = nwis.get_dv(
sites=site_id,
start=start_str,
end=end_str,
parameterCd="00060",
)