upgrade nextjs, preact, mdx-bundler, esbuild

data/blog/github-markdown-guide.mdx

@@ -153,6 +153,18 @@ function fancyAlert(arg) {
 }
 ```
 
+## Footnotes
+
+```
+Here is a simple footnote[^1]. With some additional text after it.
+
+[^1]: My reference.
+```
+
+Here is a simple footnote[^1]. With some additional text after it.
+
+[^1]: My reference.
+
 ## Task Lists
 
 ```