Bump highlight.js from 9.17.1 to 10.4.1 in /book/8-begin

Bumps [highlight.js](https://github.com/highlightjs/highlight.js) from 9.17.1 to 10.4.1.
- [Release notes](https://github.com/highlightjs/highlight.js/releases)
- [Changelog](https://github.com/highlightjs/highlight.js/blob/master/CHANGES.md)
- [Commits](highlightjs/highlight.js@9.17.1...10.4.1)

Signed-off-by: dependabot[bot] <support@github.com>

book/8-begin/package.json

@@ -27,7 +27,7 @@
     "handlebars": "4.7.6",
     "he": "1.2.0",
     "helmet": "4.1.0-rc.2",
-    "highlight.js": "10.1.2",
+    "highlight.js": "10.4.1",
     "isomorphic-unfetch": "^3.0.0",
     "lodash": "4.17.20",
     "marked": "1.1.1",