ZNB20 broken

[giulioungaretti]

PR #403 broke the driver.

<ipython-input-5-ec0134710055> in <module>()
----> 1 Vna1 = vna1.ZNB20('networkana1', 'TCPIP0::172.20.2.142::inst0::INSTR')

c:\users\triton4acq\anaconda3\envs\qcodes-qdev-master\lib\site-packages\qcodes\instrument\metaclass.py in __call__(cls, server_name, *args, **kwargs)
     32         """
     33         if server_name is None:
---> 34             instrument = super().__call__(*args, **kwargs)
     35         else:
     36             warnings.warn('Multiprocessing is in beta, use at own risk',

c:\users\triton4acq\anaconda3\envs\qcodes-qdev-master\lib\site-packages\qcodes\instrument_drivers\rohde_schwarz\ZNB20.py in __init__(self, name, address, **kwargs)
    111                            stop=self.stop(),
    112                            npts=self.npts(),
--> 113                            parameter_class=FrequencySweep)
    114 
    115         self.add_function('reset', call_cmd='*RST')

c:\users\triton4acq\anaconda3\envs\qcodes-qdev-master\lib\site-packages\qcodes\instrument\base.py in add_parameter(self, name, parameter_class, **kwargs)
    368         if name in self.parameters:
    369             raise KeyError('Duplicate parameter name {}'.format(name))
--> 370         param = parameter_class(name=name, instrument=self, **kwargs)
    371         self.parameters[name] = param
    372 

c:\users\triton4acq\anaconda3\envs\qcodes-qdev-master\lib\site-packages\qcodes\instrument_drivers\rohde_schwarz\ZNB20.py in __init__(self, name, instrument, start, stop, npts)
     17     """
     18     def __init__(self, name, instrument, start, stop, npts):
---> 19         super().__init__(name)
     20         self._instrument = instrument
     21         self.set_sweep(start, stop, npts)

TypeError: __init__() missing 2 required positional arguments: 'names' and 'shapes'