Passing no callback to request so as to retrieve a stream causes crash

[angadn]

I think https://github.com/gitterHQ/request-http-cache/blob/master/lib/index.js#L243 should be
callback && callback(null, response, body); - should this fix it? I'd have PRed, but not sure if the module would still work as expected/cache and return a stream from Redis/cache