Switch back to SVGs for the website

[juliasilge]

We probably want to switch back to SVGs for the website when we can figure it out. The current situation:

• The book will not build on MacOS because of a segfault fitting the combination of UMAP and the fda model in Section 16.5
• On Ubuntu, I have not figured out how to get nice fonts for SVGs. It uses some random font and then the SVGs fall back to Times.

[juliasilge]

Related to the segfault, we do get some kind of error on Ubuntu, but not one that crashes everything:

✔ 11 of 15 tuning:     umap_bayes (4m 24.3s)
i 12 of 15 tuning:     umap_fda
malloc(): invalid size (unsorted)
✔ 12 of 15 tuning:     umap_fda (4m 48.1s)
i 13 of 15 tuning:     umap_rda
✔ 13 of 15 tuning:     umap_rda (4m 28.6s)
i 14 of 15 tuning:     umap_bag
✔ 14 of 15 tuning:     umap_bag (4m 24.4s)
i 15 of 15 tuning:     umap_mlp
✔ 15 of 15 tuning:     umap_mlp (4m 45.2s)
Warning message:
In mclapply(argsList, FUN, mc.preschedule = preschedule, mc.set.seed = set.seed,  :
  scheduled core 2 did not deliver a result, all values of the job will be affected