Matplotlib 3.4 deprecated calling plt.gca() with parameters, which the plot module does in scatter3d()

[JS3xton]

Matplotlib 3.4 deprecated calling plt.gca() with parameters, which the FlowCal plot module does in the scatter3d() function.

With matplotlib v3.4.3 and FlowCal v1.3.0:

>>> FlowCal.plot.scatter3d(np.array([[1,2,3],[4,5,6],[7,8,9]]))

FlowCal/plot.py:3484: MatplotlibDeprecationWarning: Calling gca() with keyword arguments was deprecated in Matplotlib 3.4. Starting two minor releases later, gca() will take no keyword arguments. The gca() function should only be used to get the current axes, or if no axes exist, create new axes with default keyword arguments. To create a new axes with non-default arguments, use plt.axes() or plt.subplot().