make sure all vignettes generated locally not on CRAN

From Brian Ripley:

This has added Suggests: rstan but does not use it conditionally, so on an M1 Mac

Packages suggested but not available for checking:
   'brms', 'rstan', 'rstanarm', 'rstantools'
...
--- re-building ‘large-data.Rmd’ using rmarkdown
Quitting from lines 45-48 (large-data.Rmd)
Error: processing vignette 'large-data.Rmd' failed with diagnostics:
there is no package called 'rstan'

This is because rstan requires package V8 hence v8, probably the hardest of all external software to install and no one has yet succeeded in porting to arm64.

Author: jgabry

DESCRIPTION

@@ -1,8 +1,8 @@
 Package: loo
 Type: Package
 Title: Efficient Leave-One-Out Cross-Validation and WAIC for Bayesian Models
-Version: 2.4.0
-Date: 2020-12-01
+Version: 2.4.1
+Date: 2020-12-07
 Authors@R: c(person("Aki", "Vehtari", email = "[email protected]", role = c("aut")),
              person("Jonah", "Gabry", email = "[email protected]", role = c("cre", "aut")),
              person("Mans", "Magnusson", role = c("aut")),

NEWS.md

@@ -1,3 +1,8 @@
+# loo 2.4.1
+
+Fixes issue reported by CRAN where one of the vignettes errored on an M1 Mac
+due to RStan's dependency on V8. 
+
 # loo 2.4.0
 
 ### Bug fixes 

vignettes/loo2-large-data.Rmd

@@ -13,6 +13,9 @@ params:
 %\VignetteIndexEntry{Using Leave-one-out cross-validation for large data}
 -->
 
+```{r settings, child="children/SETTINGS-knitr.txt"}
+```
+
 ```{r, child="children/SEE-ONLINE.txt", eval = if (isTRUE(exists("params"))) !params$EVAL else TRUE}
 ```
 

vignettes/loo2-with-rstan.Rmd

@@ -13,6 +13,9 @@ params:
 %\VignetteIndexEntry{Writing Stan programs for use with the loo package}
 -->
 
+```{r settings, child="children/SETTINGS-knitr.txt"}
+```
+
 ```{r, child="children/SEE-ONLINE.txt", eval = if (isTRUE(exists("params"))) !params$EVAL else TRUE}
 ```