Fixes "alt" tag not showing, when images option is used (#210)

* Fixes "alt" tag not showing
Issue -> hexojs/hexo-renderer-markdown-it/#205

* add test code

---------

Co-authored-by: uiolee <22849383+uiolee@users.noreply.github.com>

Author: benwinding

lib/images.js

@@ -13,6 +13,8 @@ function images(md, opts) {
     const token = tokens[idx];
     const { postPath } = env;
 
+    token.attrSet('alt', token.content);
+
     if (lazyload) {
       token.attrSet('loading', 'lazy');
     }

test/index.js

@@ -118,7 +118,7 @@ describe('Hexo Renderer Markdown-it', () => {
       const resultInline = renderer.render({ text }, { inline: true });
       resultBlock.should.eql('<p>inline text</p>\n');
       resultInline.should.eql('inline text');
-    })
+    });
   });
 
   describe('plugins', () => {
@@ -403,6 +403,15 @@ describe('Hexo Renderer Markdown-it', () => {
       result.should.eql('<p><img src="/blog/bar/baz.jpg" alt=""></p>\n');
     });
 
+    it('alt text', () => {
+      hexo.config.markdown.images = { test: true };
+
+      const renderer = new Renderer(hexo);
+      const result = renderer.render({ text: '![alt text](/bar/baz.jpg)' });
+
+      result.should.eql('<p><img src="/bar/baz.jpg" alt="alt text"></p>\n');
+    });
+
     describe('post_asset', () => {
       const Post = hexo.model('Post');
       const PostAsset = hexo.model('PostAsset');