Hack needed to workaround devtools-related vignette building failure

[ldemaz]

After upgrading from an earlier version of R I used for building geospaar, I found that unit2-module2 was failing to build when running devtools::install_github (or remotes::...) or devtools::install. The error message that cropped up was the same as in this GitHub issue, and other similar ones. Ultimately, it was this:

> Error in (function (command = NULL, args = character(), error_on_status = TRUE,  : 
>   System command error

The references I have found to this issue, however, seem mostly related to windows installs. In this case, the problem seems to be some interaction with raster package functions applied to *StackBricks. The error thrown above this was along the lines of "incorrect number of layer names". The hack I reference here allows me to get around it, but it is rather ungainly. Note that this issue only occurs when building vignettes. The Rmarkdown knits fine, and there is no error when the original code ran in the chunk.

geospaar/vignettes/unit2-module2.Rmd

Line 416 in 19b2cea

```{r, echo=FALSE}

The error appeared in another place also. Basically the same error, but to fix it I had to remove quotes from around the vector of function names passed into the lapply.

[ldemaz]

After another round of package updates, got the same error again. This time, I fixed it by changing this line back to have quoted functions. Unstable.

@LLeiSong can you check the build on Windows, please?