Update mdbook to 0.4.15

Author: ISSOtm

.github/workflows/build-and-deploy.yml

@@ -17,7 +17,7 @@ on:
     - cron: '42 16 1/7 * *'
 
 env:
-  MDBOOK_LINKCHECK_VER: 0.7.4
+  MDBOOK_LINKCHECK_VER: 0.7.6
 
 jobs:
   build:
@@ -31,7 +31,7 @@ jobs:
     - name: Install mdbook
       uses: peaceiris/actions-mdbook@v1
       with:
-        mdbook-version: 0.4.12
+        mdbook-version: 0.4.15
 
     # FIXME: Keep this up to date
     - name: Install mdbook-linkcheck