fetch command returns SeriesBlock with improper "duration" value

the duration in the returned SeriesBlock is the duration of a single block, but it should be equal to the total number of seconds of data fetched:

In [1]: from arrakis import fetch

In [2]: d = fetch(["H1:CAL-DELTAL_EXTERNAL_DQ"], 1407005100, 1407005104)

In [3]: d.duration
Out[3]: 0.0625

In [4]: d["H1:CAL-DELTAL_EXTERNAL_DQ"].duration
Out[4]: 0.0625

In [5]: d["H1:CAL-DELTAL_EXTERNAL_DQ"].sample_rate
Out[5]: 16384

In [6]: d["H1:CAL-DELTAL_EXTERNAL_DQ"].data.shape
Out[6]: (65536,)