Errors with sampling frequency for open data

There is a problem when setting values of sampling frequency that are not equal to a power of 2.

Fails with the following,

~/anaconda3/lib/python3.6/site-packages/bilby-0.4.4-py3.6.egg/bilby/gw/source.py in _base_lal_cbc_fd_waveform(frequency_array, mass_1, mass_2, luminosity_distance, theta_jn, phase, a_1, a_2, tilt_1, tilt_2, phi_12, phi_jl, lambda_1, lambda_2, eccentricity, **waveform_kwargs)
    263     h_cross = np.zeros_like(frequency_array, dtype=np.complex)
    264 
--> 265     h_plus[:len(hplus.data.data)] = hplus.data.data
    266     h_cross[:len(hcross.data.data)] = hcross.data.data
    267 

ValueError: could not broadcast input array from shape (16385) into shape (8197)

Until a permanent fix, setting sampling frequency equal to a power of 2 should avoid this problem.

@colm.talbot @gregory.ashton