fix replicate.stream example

[zeke]

The docs for replicate.stream() don't have any input:

for await (const event of replicate.stream("meta/llama-2-70b-chat")) {
    process.stdout.write(`${event}`);
}

See https://github.com/replicate/replicate-javascript/tree/6dd5b21884e5dab8d137818e3c43ab14f4335f30#replicatestream

Let's update this to a working example.

[zeke]

Like this:

const input = {
  prompt: "Can you write a poem about open source machine learning?",
}

for await (const event of replicate.stream("meta/llama-2-70b-chat", { input })) {
  process.stdout.write(event.toString());
};