docs: update preview image's font-matter

Author: cotes2020

_posts/2019-08-08-text-and-typography.md

@@ -9,7 +9,7 @@ tags: [typography]
 math: true
 mermaid: true
 image:
-  src: /commons/devices-mockup.png
+  path: /commons/devices-mockup.png
   width: 800
   height: 500
 ---

_posts/2019-08-08-write-a-new-post.md

@@ -221,12 +221,12 @@ The output will be:
 
 ### Preview Image
 
-If you want to add an image to the top of the post contents, specify the attribute `src`, `width`, `height`, and `alt` for the image:
+If you want to add an image to the top of the post contents, specify the attribute `path`, `width`, `height`, and `alt` for the image:
 
 ```yaml
 ---
 image:
-  src: /path/to/image/file
+  path: /path/to/image/file
   width: 1000   # in pixels
   height: 400   # in pixels
   alt: image alternative text
@@ -235,7 +235,7 @@ image:
 
 Except for `alt`, all other options are necessary, especially the `width` and `height`, which are related to user experience and web page loading performance. The above section "[Size](#size)" also mentions this.
 
-Starting from _Chirpy v5.0.0_, the attributes `height` and `width` can be abbreviated: `height` → `h`, `width` → `w`. In addition, the [`img_path`](#image-path) can also be passed to the preview image, that is, when it has been set, the  attribute `src` only needs the image file name.
+Starting from _Chirpy v5.0.0_, the attributes `height` and `width` can be abbreviated: `height` → `h`, `width` → `w`. In addition, the [`img_path`](#image-path) can also be passed to the preview image, that is, when it has been set, the  attribute `path` only needs the image file name.
 
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