Fix danger to lookup comment for its own only

[kwonoj]

• closes unique identifier for danger-written comments? #269 .

This PR updates logics of getDangerCommentID, in addition to look up userid of given danger token but also looks for comment body if it has comment signature written via danger. For cases of user shares token for danger runner, it'll prevent comment is being deleted by danger looks up comment not written by itself.

Instead of introducing new hidden comment identifier, I took simple paths of looking signature directly (including HTML tags), which is sufficiently unique that individual user won't write those in their own comment.

[macklinu]

Just reading through the code changes, this is a really cool idea! I like the approach. 😃

[orta]

This looks 👍 to me too - thanks @kwonoj

Bit surprised by the red, just re-ran it - should be fine if not, I'll throw an hour or two at danger tomorrow morning to try get these builds determinate

[kwonoj]

@orta seems it's continuously failing on travis (https://travis-ci.org/danger/danger-js/builds) by looking history, and log says jest-cli is missing, yarn does install pkg some way unexpected?

[orta]

Alright, well I'll merge this for now as it's not due to your PR 👍