amend! LWT toplevel example: do not generate a source map

LWT toplevel example: do not include sources in a source map

Outputting this source map would fail on 32-bit architectures since
its size, once Base64-encoded, would be over the string length limit
of 16 MiB.

toplevel/examples/lwt_toplevel/dune

@@ -40,9 +40,11 @@
  (modes byte js)
  (js_of_ocaml
   (link_flags
-   :standard
    ; The source map would be too large on 32-bit architectures otherwise
-   --no-source-map)
+   :standard
+   --source-map
+   \
+   --source-map-inline)
   (build_runtime_flags
    (:standard
     --file