rustdoc: change aliases attribute to data-aliases

The "aliases" attribute is not listed [on MDN], so it sounds like
it's rustdoc-specific. We don't want to conflict with any attributes
that are added to the spec in the future.

[on MDN]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Heading_Elements

src/librustdoc/html/render/mod.rs

@@ -1546,7 +1546,7 @@ fn render_impl(
         let aliases = if aliases.is_empty() {
             String::new()
         } else {
-            format!(" aliases=\"{}\"", aliases.join(","))
+            format!(" data-aliases=\"{}\"", aliases.join(","))
         };
         if let Some(use_absolute) = use_absolute {
             write!(