Cache middleware fails to intercept response if chunkedResponse is enabled

When a cache (like [https://github.com/tomdale/fastboot-redis-cache](fastboot-redis-cache)) is provided, the Express server [builds middleware](https://github.com/ember-fastboot/fastboot-app-server/blob/master/src/express-http-server.js#L70-L87) to read/write cache entries.

To grab responses, it replaces the implementation of `res.send` with one that stores to the cache [here](https://github.com/ember-fastboot/fastboot-app-server/blob/master/src/express-http-server.js#L89-L108).

When chunked responses are enabled `res.write` is called instead of `res.send`, so nothing is ever written to the cache.

Using something like https://github.com/axiomzen/express-interceptor (or implementing similar techniques) would solve this issue.