fix: use class is function on ipns

[vasco-santos]

As instance of fails using different versions of a module, it was changed to use class-is.

Needs:

• js-peer-id#84
• interface-datastore#24

Fixes #1615

[fsdiogo]

LGTM 👍

[lidel]

LGTM

I tested this with ipfs/interface-datastore#24 in the context of ipfs-companion (#1615) and the fix works as expected, datastore key does not have a valid format error is gone.

[alanshaw]

LGTM but needs tests e.g. https://codecov.io/gh/ipfs/js-ipfs/src/master/src/core/ipns/publisher.js#L53...59

[vasco-santos]

@alanshaw the peerId instance is obtained through js-ipfs/core/ipns/publisher.js#L33. Considering that _putRecordToRouting is a private function js-ipfs/core/ipns/publisher.js#L53 maybe we should remove this validation. The previous tests did not hit those lines, as well.

I am not able to test this, unless I test the private functions directly or mock the PeerId.createFromPrivKey function. However, if I mock it, it will stop immediately in the first case that is hit, and the others will not be covered.