v2.9.7

Bugfixes:

• Fix promisify not retaining custom properties of the function. This enables promisifying the "request" module's export function and its methods at the same time.
• Fix promisifyAll methods being dependent on this when they are not originally dependent on this. This enables e.g. passing promisified fs functions directly as callbacks without having to bind them to fs.
• Fix process.nextTick being used over setImmediate in node.