chai-fs destroys any existing assertion handler for .with()

[bluepichu]

In my case, this is causing issues with chai-spies. For example, this passes fine:

let spies = require("chai-spies");
let fs = require("chai-fs");
let chai = require("chai");

chai.use(fs).use(spies);

let { spy, expect } = chai;

it("should still let me use chai-spies' .with() assertions", async () => {
	let fn = spy((arg) => arg + 1);

	let x = fn(2);

	expect(x).to.equal(3);
	expect(fn).to.have.been.called.once;
	expect(fn).to.have.been.called.with(2);
});

But this fails:

let spies = require("chai-spies");
let fs = require("chai-fs");
let chai = require("chai");

chai.use(spies).use(fs); // <--- the only change is the order on this line

let { spy, expect } = chai;

it("should still let me use chai-spies' .with() assertions", async () => {
	let fn = spy((arg) => arg + 1);

	let x = fn(2);

	expect(x).to.equal(3);
	expect(fn).to.have.been.called.once;
	expect(fn).to.have.been.called.with(2);
});

Output:

  1) should still let me use chai-spies' .with() assertions:
     TypeError: expect(...).to.have.been.called.with is not a function
      at Context.it (spec.js:18:37)