cache-control header isn't sent when `maxAge` value is 0

[Husam Harazi]

If you specify 0 as the maxAge value in the options object, the header won't get send.

That's because it will check for truthy values to determine if the header should be set or not.

https://github.com/Ceicc/range/blob/3957f7c30741919ce8e89082e1a4373d5e1b256b/index.js#L171