buffer@4
Node.js removed the buffer.toArrayBuffer() API sometime during node 0.11. Users who rely on it will have code that doesn't work in node.js, which is unfortunate.
feross/buffer v4.0.0 removed buffer.toArrayBuffer() to have parity with node.js.
Going forward, users can just use buffer.buffer to get an ArrayBuffer since Buffer is just a subclass of Uint8Array in both node.js and the browser.
This is a breaking change, since we're removing a method from the buffer.
I'm only sending this PR now, since buffer v4.1.0 has a 30% performance increase for lots of the buffer methods and I want users to have that