Enable the tomorrow theme for Prism.

june128 · june128 · commit 21e2f4c9eba9 · 2018-12-26T00:27:09.000+01:00
Switch to the tomorrow theme for Prism syntax highlighting because it
(looks cool and) doesn't have issues with the GitBook night mode.
diff --git a/book.json b/book.json
@@ -38,6 +38,9 @@
       "ignore": [
         "emojicode",
         "text"
+      ],
+      "css": [
+        "prismjs/themes/prism-tomorrow.css"
       ]
     },
     "api-language-selector": {
