`Buffer()` without a `new` keyword is going to be hard-deprecated soon

Nobody has claimed this yet.

Refs: https://github.com/nodejs/node/pull/8169, https://github.com/nodejs/node/pull/7152.

Two options here:
- Use the new Buffer API — `Buffer.alloc()`/`Buffer.from()`/`Buffer.allocUnsafe()` (requires [a shim](https://github.com/feross/safe-buffer) for v0.10/v0.12 and older v4.x versions prior to v4.5.0).
- Use `new Buffer()` for the time being — just add the `new` keyword everywhere. You should manually check that everything is safe in this case, see the links below for more explanation. That _might_ be hard-deprecated at some later point.

More background:
- https://github.com/ChALkeR/notes/blob/master/Lets-fix-Buffer-API.md
- https://github.com/ChALkeR/notes/blob/master/Buffer-knows-everything.md
- https://github.com/nodejs/node/pull/7152#issuecomment-240880317

Quick grep (you should better re-check):

```
duplexify-3.4.5.tgz/test.js:279: t.same(chunk, Buffer('hello world'))
duplexify-3.4.5.tgz/test.js:290: dup.write(Buffer('hello world'))
```

The grep above only includes the lines that call `Buffer()` without the `new` keyword, if you choose to move to the new API — you should probably also replace `new Buffer(…)` calls.

Re-check the repository for Buffer() and new Buffer(...) calls, starting with the occurrences noted in test.js around lines 279 and 290. Read the linked Node.js Buffer guidance and choose the compatible API approach, including the stated older-version constraints. Done means the deprecated calls are addressed and the existing tests still pass.

Written by the indexing model from the issue text.