3d plot figure size is not affected by figsize

I am plotting a 3d plot, but the figure size is not changed according to my setting.
This is my code:
```
using PyPlot
using3D()
fig = plt.figure(figsize=(6, 10))
ax = plt.axes(projection="3d")
```

I am running Julia 1.5.3.

Start by reproducing the reported Julia 1.5.3 example with PyPlot, using `using3D()`, `plt.figure(figsize=(6, 10))`, and `plt.axes(projection="3d")`. Investigate how PyPlot and matplotlib handle the 3D figure size, and consider the issue resolved when the displayed 3D figure reflects the requested dimensions.

索引モデルが issue の本文から書いたものです。