Issue Colorbar placement

Hello,

I am using Plots with PyPlot as a backend for `heatmap`. The placement of the colorbar doesn't match the width of the heatmap (see picture) also I can't move the position of the colorbar.
The first issue is resolved when I switch to GR as a backend but not the second.

Here is the same issue https://github.com/JuliaPlots/Plots.jl/issues/1755

Here is my code:

```
using Plots
pyplot()

x = randn(10,200)
heatmap(x, color = :inferno, colorbar = :bottom)
```

Result:
[picture.pdf](https://github.com/JuliaPy/PyPlot.jl/files/4660040/picture.pdf)

Start by reproducing the reported heatmap with the PyPlot backend using `pyplot()`, `colorbar = :bottom`, and the provided 10x200 random array. Read the linked Plots.jl issue for related context and compare the PyPlot and GR results. Done means the colorbar matches the heatmap width and its position can be controlled consistently.

Scritto dal modello di indicizzazione a partire dal testo della issue.