Fix doc for unwatch() and close().

[tamuratak]

.unwatch() does not return a promise. .close() does.

chokidar/index.js

Lines 494 to 496 in 820ab96

	return this;
	}

chokidar/index.js

Lines 521 to 524 in 820ab96

	this._closePromise = closers.length ? Promise.all(closers).then(() => undefined) : Promise.resolve();
	return this._closePromise;
	}