Enforce `arguments` constraint reflexively

My personal preference would be for `eql` to be *more* lax (as opposed to less)--considering `arguments` objects as equivalent to arrays if their elements are deeply equal. Since this project uses Node.js's `deepEqual` logic, I assume this is not the intention of `eql`. The important thing is consistency, as a patch like 7c2052351263ddeb7afe2018dbd9d040ad8bf2e9 should not have [effected downstream libraries](https://github.com/MatthewMueller/cheerio/pull/350).

Commit message:

> If an `arguments` object is not considered `eql` to an array, then the
> inverse should also hold true.