fix: Pull in latest mdbook

Author: epage

.github/workflows/book.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Setup
         uses: peaceiris/actions-mdbook@v1
         with:
-          mdbook-version: '0.4.5'
+          mdbook-version: '0.4.14'
       - name: Build
         run: mdbook build
       - name: Deploy