Fix failing snapshots test: topo.pattern.basic.rectangular was removed, but it's the default value for PowerSpectrum.windowing_function in the test snapshot. I'm assuming nobody cares about that.
Fix failing snapshots test: topo.pattern.basic.rectangular was removed, but it's the default value for PowerSpectrum.windowing_function in the test snapshot. I'm assuming nobody cares about that.

mjabri/topographica,mjabri/topographica,Tasignotas/topographica_mirror,ioam/topographica,Tasignotas/topographica_mirror,mjabri/topographica,ioam/topographica,ioam/topographica,Tasignotas/topographica_mirror,Tasignotas/topographica_mirror,mjabri/topographica,mjabri/topographica,ioam/topographica,Tasignotas/topographica_mirror,ioam/topographica