fix auth-in-url (#576)

Author: mbostock

src/client/sidebar-init.ts

@@ -1,3 +1,6 @@
+// Remove basic authentication in the URL, if any (to fix file attachments).
+if (Object.assign(document.createElement("a"), {href: ""}).password) location.replace(location.href);
+
 const sidebar = document.querySelector<HTMLElement>("#observablehq-sidebar")!;
 const toggle = document.querySelector<HTMLInputElement>("#observablehq-sidebar-toggle")!;