replaced webgl by rgl to make vignette much smaller

vignettes/spcosa.Rmd

 ---
 title: "Spatial Coverage Sampling with spcosa"
 author: "Dennis Walvoort"
-date: "2018-01-19"
+date: "2021-01-06"
 output: 
   rmarkdown::html_vignette:
     toc: true
@@ -15,7 +15,7 @@ vignette: >
 
 ```{r, echo=FALSE}
 if (requireNamespace("rgl", quietly = TRUE)) {
-  knitr::knit_hooks$set(webgl = rgl::hook_webgl)
+  knitr::knit_hooks$set(rgl = rgl::hook_rgl)
 }
 knitr::opts_chunk$set(comment = NA)
 set.seed(314)
@@ -485,7 +485,7 @@ plot(strata)
 plot(strata_crs)
 ```
 
-Note that `grd` seems to have more compact strata near the geographic poles than `grd_crs`. However, the contrary is true. This becomes evident when both stratifications are projected on a sphere (use your mouse to interact with these spheres):
+Note that `grd` seems to have more compact strata near the geographic poles than `grd_crs`. However, the contrary is true. This becomes evident when both stratifications are projected on a sphere:
 
 
 
@@ -539,7 +539,7 @@ function(x) {
 }
 ```
 
-```{r, eval=requireNamespace("rgl", quietly = TRUE), echo=FALSE, results='hide', fig.width=5, fig.height=3, webgl=TRUE,dpi=72}
+```{r, eval=requireNamespace("rgl", quietly = TRUE), echo=FALSE, results='hide', fig.width=7, fig.height=4, rgl=TRUE}
 rgl::open3d(userMatrix = rbind(
     c( 0.73, -0.63, 0.25, 0),
     c( 0.37,  0.69, 0.63, 0),