bug in FSFModel.get_cube()

[nfbouche]

when using lbda in Angstrom, the line

def get_3darray(self, lbda, shape, center=None):
    """Return FSF cube at the given wavelengths."""
    return Moffat2D(self.get_fwhm(lbda, unit='pix'), self.get_beta(lbda),
                    shape, center)

should be

def get_3darray(self, lbda, shape, center=None):
    """Return FSF cube at the given wavelengths."""
    return Moffat2D(self.get_fwhm(lbda), self.get_beta(lbda),
                    shape, center)