The formatUpdated config doesn't display any thing

[immortalt]

Bug Report

You can see in this page's code:
https://github.com/immortal-blog/immortal-blog.github.io/blob/main/docs/index.html
and you can see that all pages don't have update time:
https://immortal-blog.github.io/#/golang/migrate-mgo-to-qmgo
I added the config as the doc mentioned,

window.$docsify = {
                formatUpdated: '{YYYY}-{MM}-{DD}',

but I still can't see any change in my blog. There is no time.
(I'm sure that I cleaned the cache before refreshing the page)

Steps to reproduce

1. Create a Github Page using docsify like https://immortal-blog.github.io/#/, or you can just fork this git.
2. Add the config option: formatUpdated: '{YYYY}-{MM}-{DD}'.
3. Clean the browser cache and refresh the Github Page.

What is current behaviour

Nothing changed.
There is no update time on the page.

What is the expected behaviour

There is an update time on the page.

Other relevant information

• Bug does still occur when all/other plugins are disabled?

• Your OS: Ubuntu 20.04 LTS

• Node.js version: v14.16.1

• npm/yarn version: 7.12.0

• Browser version: Firefox 88.0.1 x64

• Docsify version: 4.4.3

• Docsify plugins: disabled all

Please create a reproducible sandbox

Mention the docsify version in which this bug was not present (if any)

[sy-records]

you need add {docsify-updated}

    window.$docsify = {
        formatUpdated: '{YYYY}-{MM}-{DD}',
        name: 'Immortal Blog',
        repo: '',
        auto2top: true,
        coverpage: true,
        loadSidebar: true,
        maxLevel: 4,
        subMaxLevel: 2,
+        plugins: [
+            function(hook, vm) {
+                hook.beforeEach(function(html) {
+                    return (
+                        html +
+                        '\n----\n' +
+                        'Last modified {docsify-updated}'
+                    );
+                });
+            }
+        ]
+    }

[immortalt]

you need add {docsify-updated}

    window.$docsify = {
        formatUpdated: '{YYYY}-{MM}-{DD}',
        name: 'Immortal Blog',
        repo: '',
        auto2top: true,
        coverpage: true,
        loadSidebar: true,
        maxLevel: 4,
        subMaxLevel: 2,
+        plugins: [
+            function(hook, vm) {
+                hook.beforeEach(function(html) {
+                    return (
+                        html +
+                        '\n----\n' +
+                        'Last modified {docsify-updated}'
+                    );
+                });
+            }
+        ]
+    }

It seems that the problem solved. Thanks!
But I think docsify's doc needs to add this info, otherwise other user will also meet this problem and waste some time again and again.
The doc that needs to be completed is here: https://docsify.js.org/#/configuration?id=formatupdated.

[sy-records]

Here's an example https://github.com/docsifyjs/docsify/blob/develop/docs/write-a-plugin.md#edit-button