Fix build failure due to label warning

[laaksonel]

Compilation fails due to unlabeled argument p

rescript: [6/6] client/client.cmj
FAILED: client/client.cmj

  Warning number 6 (configured as error)
  .../dream/example/w-fullstack-rescript/client/client.res:14:11-29

  12 │     let p = document->Document.createElement("p")
  13 │     p->Element.setInnerText(text)
  14 │     body->Element.appendChild(p)
  15 │   }
  16 │ }

  label child was omitted in the application of this function.