lambda-local as endpoint for aws-sdk

aws-sdk sends requests as `'content-type': 'binary/octet-stream'`, which watch doesn't support.
Would you accept a PR that uses raw-body to handle those requests?

```js
await lambdaLocal.execute({
	event: JSON.parse((await getRawBody(ctx.req)).toString()),
	lambdaPath: '...',
});
```