`entriesEqual` breaks on sets of objects with null prototype

[demurgos]

The last line of entriesEqual throws the following error in my test cases:

TypeError: Cannot convert object to primitive value
    at Array.toString (native)
    at Array.sort (native)
[...]

Here is how I can reproduce it with chai:

function getAnimals() {
  const duck = Object.create(null);
  duck.name = "duck";
  const cat = Object.create(null);
  cat.name = "cat";
  return new Set([duck, cat]);
}

const actual = getAnimals();
const expected = new Set([{name: "duck"}, {name: "cat"}]);

assert.deepEqual(actual, expected);

The error is caused by the fact that the objects with a null prototype cannot be converted to strings implicitly, and the array sort function performs a lexicographical sort on strings so it first tries to convert them to strings.

(Tested on Node 9.4)