Shear_wave_fraction not being called in parallel

[taranye96]

In generate_ruptures_parallel.run_parallel_generate_ruptures(), it takes the shear_wave_fraction as a parameter, but it does not use the parameter when calling get_rupture_onset() function in line 226. So, it looks like it just keeps using the default shear_wave_fraction of 0.7 instead of the parameter we set.