Update the path of html_playground_url in playground.md

Author: HosseinAssaran

src/meta/playground.md

@@ -50,4 +50,4 @@ Playground. This feature is enabled if you use the `#[doc]` attribute called
 [mdbook]: https://github.com/rust-lang/mdBook
 [official-rust-docs]: https://doc.rust-lang.org/core/
 [rustdoc-book]: https://doc.rust-lang.org/rustdoc/what-is-rustdoc.html
-[html-playground-url]: https://doc.rust-lang.org/rustdoc/the-doc-attribute.html#html_playground_url
+[html-playground-url]: https://doc.rust-lang.org/rustdoc/write-documentation/the-doc-attribute.html#html_playground_url