feat: Configure for Rails v8

Author: toshimaru

Diff for: _config.yml

@@ -2,11 +2,13 @@ title: RailsDoc(β)
 description: Ruby on Rails API Documentation.
 url: https://railsdoc.github.io
 source: src
-default_rails_version: "7.2.2"
+default_rails_version: "8.0.0"
 rails_versions:
+  "8.0":
+    specific_version: "8.0.0"
+    latest: true
   "7.2":
     specific_version: "7.2.2"
-    latest: true
   "7.1":
     specific_version: "7.1.5"
   "7.0":
@@ -31,10 +33,15 @@ defaults:
   - scope:
       path: ""
     values:
-      version: 7.2
+      version: 8.0
       image: https://avatars.githubusercontent.com/u/4223
       toc: true
       root_path: "/"
+  - scope:
+      path: "7.2"
+    values:
+      version: 7.2
+      root_path: "/7.2/"
   - scope:
       path: "7.1"
     values: