.eql() is broken in ES6

[teppeis]

Following tests should not pass, but pass in Node v4+ and modern browsers that support ES6.

expect('a').to.be.eql(['a']);
expect('a').to.be.eql({0: 'a'});
expect(1).to.be.eql({});
expect(true).to.be.eql({});

Change of Object.keys in ES6 causes this issue.
I've fixed same issues in Node.js core assert.deepEqual and commonjs-assert.

[pomle]

Was there a test for this in expect that used eql()?

[larsgw]

expect([]).to.eql({})

This passes as well, although that may be intended behaviour.

[Kequc]

expect({ a: '1' }).to.eql({ a: 1 })

This also passes. I understand it's because the two values loosely equal one another but maybe there could be a separate method for comparing objects?