Fix path to static resources

In production deployments, the static assets are stored in
`/usr/local/share/receipts/static`.  The working directory is
`/usr/local/share/receipts`, so using a relative path of `static` is
sufficient.  We can use the same path in development with a symlink
pointing to the `esbuild` output directory.

src/main.rs

@@ -251,6 +251,6 @@ async fn rocket() -> _ {
                 update_transaction
             ],
         )
-        .mount("/static", FileServer::from("js/dist"))
+        .mount("/static", FileServer::from("static"))
         .attach(Template::fairing())
 }

static

@@ -0,0 +1 @@
+js/dist