Add response return to ChatStream

[ytimocin]

Added response return to ChatStream.

Fixes: #50

[ytimocin]

Both unit tests and chat_with_streaming example pass with and without this one.

[sublimator]

This is not necessary. You are supposed to use as so:

client-js/examples/chat_with_streaming.js

Lines 1 to 18 in 6499236

	import MistralClient from '@mistralai/mistralai';
	const apiKey = process.env.MISTRAL_API_KEY;
	const client = new MistralClient(apiKey);
	const chatStreamResponse = await client.chatStream({
	model: 'mistral-tiny',
	messages: [{role: 'user', content: 'What is the best French cheese?'}],
	});
	console.log('Chat Stream:');
	for await (const chunk of chatStreamResponse) {
	if (chunk.choices[0].delta.content !== undefined) {
	const streamText = chunk.choices[0].delta.content;
	process.stdout.write(streamText);
	}
	}