[Symbol.toStringTag] getter seems to interfer with chai's deep.equal check

[Gozala]

As per ipld/js-ipld-dag-pb#184 (comment) it appears that chai will deep equality check with duck typed counterpart of the instance because of the [Symbol.toStringTag] getter this library adds.

I have created pull request to illustrate this #26, although this library uses jest instead of chai same issue appears to manifest. Unwapped class does not seem to exhibit this behavior.