Update to last reveal.js 4.2.1 (#148)

diff --git a/inst/reveal.js-4.2.1/examples/assets/image2.png b/inst/reveal.js-4.2.1/examples/assets/image2.png
new file mode 100644
index 0000000..6c403a0
--- /dev/null
+++ b/inst/reveal.js-4.2.1/examples/assets/image2.png
Binary files differ