Issues with plot_voronoi(backend = "interp")

[GegznaV]

In plotting.Rmd vignette there were issues on Linux, if these lines were used:

```{r uneven-II, fig.cap=CAPTION}
plot_voronoi(uneven)
```

And this option solved the issue.

```{r uneven-II, fig.cap=CAPTION}
plot_voronoi(uneven, backend = "deldir")
```

From time to time on my Windows, there were also issues with the first line when the new backend package "interp" (currently it is the default) in latticeExtra was used. More details about the new backed in the documentation of latticeExtra v0.6-30:

?latticeExtra::panel.voronoi

The functionality of the new backend should and hyperSpec should be investigated in more detail.