fix(core): update

ts/index.ts

@@ -1,4 +1,4 @@
-import * as plugins from './smartmarkdown.plugins';
+import * as plugins from './smartmarkdown.plugins.js';
 
 export class SmartMarkdown {
   constructor() {}
@@ -9,9 +9,9 @@ export class SmartMarkdown {
    */
   public async markdownToHtml(mdString: string): Promise<string> {
     const result = await plugins
-      .remark()
-      .use(plugins.remarkHtml)
-      .use(plugins.remarkFrontmatter, ['yaml', 'toml'])
+      .remark.remark()
+      .use(plugins.remarkHtml.default)
+      .use(plugins.remarkFrontmatter.default, ['yaml', 'toml'])
       .process(mdString);
     return result.toString();
   }