fix(修复错误调用React HOOK的问题):

(cherry picked from commit 03408d4d65a52a1388d9fc251c45a624ff056766)

themes/example/index.js

@@ -156,6 +156,7 @@ const LayoutPostList = props => {
 const LayoutSlug = props => {
   const { post, lock, validPassword } = props
   const router = useRouter()
+  const waiting404 = siteConfig('POST_WAITING_TIME_FOR_404') * 1000
   useEffect(() => {
     // 404
     if (!post) {
@@ -170,7 +171,7 @@ const LayoutSlug = props => {
             }
           }
         },
-        siteConfig('POST_WAITING_TIME_FOR_404') * 1000
+        waiting404
       )
     }
   }, [post])