Compress arraybuffer example

[jakearchibald]

https://github.com/wicg/compression/blob/master/explainer.md#deflate-compress-an-arraybuffer-to-a-uint8array

It could be:

function compressArrayBuffer(input) {
  const stream = new Blob(input)
    .stream()
    .pipeThrough(new CompressionStream('deflate'));
  return new Response(stream).arrayBuffer();
}

I guess it's a little hacky, but the following example already uses blob/response, so maybe it's ok?

[jakearchibald]

PR https://github.com/WICG/compression/pull/30