Add missing detection_snr argument

Created by: dethodav

This PR addresses #1614 to correctly pass the detection_snr argument to inspiral_range.range().

With this update, the inspired_range() function returns sensible values:

>>> from gwosc.datasets import event_gps
>>> from gwpy.timeseries import TimeSeries
>>> from gwpy.astro import sensemon_range, inspiral_range
>>>
>>> gps = event_gps("GW150914")
>>> data = TimeSeries.fetch_open_data('L1', gps-32, gps+32, cache=True)
>>>
>>> psd = data.psd(4,2)
>>>
>>> snrs = [2,8,16]
>>> fmin = 10
>>> fmax = 100
>>>
>>> for s in snrs:
...     print('SNR = %d'%s)
...     r_sensemon = sensemon_range(psd, fmin=fmin, fmax=fmax, snr=s)
...     r_astro = inspiral_range(psd, fmin=fmin, fmax=fmax, snr=s)
...     print('sensemon range: %.2f Mpc'%r_sensemon.value)
...     print('inspiral range: %.2f Mpc'%r_astro.value)
...     print('ratio, sensemon/inspiral: %.2f'%(r_sensemon.value/r_astro.value))
...     print()
...
SNR = 2
sensemon range: 175.12 Mpc
inspiral range: 168.06 Mpc
ratio, sensemon/inspiral: 1.04

SNR = 8
sensemon range: 43.78 Mpc
inspiral range: 42.72 Mpc
ratio, sensemon/inspiral: 1.02

SNR = 16
sensemon range: 21.89 Mpc
inspiral range: 21.42 Mpc
ratio, sensemon/inspiral: 1.02

Closes #1614