MatplotlibDeprecationWarning: savefig() got unexpected keyword argument "facecolor" which is no longer supported as of 3.3 and will become an error two minor releases later #456

Description

A deprecation warning with savefig() has been displayed for a long time and has not been solved.

/Users/yk/anaconda3/lib/python3.11/site-packages/proplot/figure.py:469: MatplotlibDeprecationWarning: savefig() got unexpected keyword argument "facecolor" which is no longer supported as of 3.3 and will become an error two minor releases later
return func(self, *args, **kwargs)

Steps to reproduce

import proplot as pplt
import numpy as np

x = np.linspace(0, 10, 100) 
y = np.sin(x)

fig, ax = pplt.subplots()
ax.plot(x,y)
ax.format(xlabel='x axis', ylabel='y axis')
fig.savefig('test.pdf')

Expected behavior: No warning

Actual behavior:

/Users/yk/anaconda3/lib/python3.11/site-packages/proplot/figure.py:469: MatplotlibDeprecationWarning: savefig() got unexpected keyword argument "facecolor" which is no longer supported as of 3.3 and will become an error two minor releases later
return func(self, *args, **kwargs)
/Users/yk/anaconda3/lib/python3.11/site-packages/proplot/figure.py:469: MatplotlibDeprecationWarning: savefig() got unexpected keyword argument "edgecolor" which is no longer supported as of 3.3 and will become an error two minor releases later
return func(self, *args, **kwargs)
/Users/yk/anaconda3/lib/python3.11/site-packages/proplot/figure.py:469: MatplotlibDeprecationWarning: savefig() got unexpected keyword argument "orientation" which is no longer supported as of 3.3 and will become an error two minor releases later
return func(self, *args, **kwargs)

Proplot version

matplotlib: 3.4.3
proplot: 0.9.7
python: 3.11
Computer: macbook pro, m2pro