License detection diffs are incorrect

It looks to me like license detection diff detection is currently failing. For example, I've added a package to a testing repository and I see this reflected in the diff
``` json
{
"status": "added",
"factors": [],
"score": 100,
"new": {
"path": "project/vendor/github.com/AndreasBriese/bbloom/LICENSE",
"type": "file",
"name": "LICENSE",
"size": 1671,
"sha1": "73e9520e4dfbadc8e525d8f38dff93a62f8623fb",
"fingerprint": "",
"original_path": "project/vendor/github.com/AndreasBriese/bbloom/LICENSE",
"licenses": [],
"copyrights": []
},
"old": null
}
```
however the licenses field is empty -- I would expect this to contain a reference to the new license I think.

I see that there was a large PR on scancode that probably modified the structure: https://github.com/nexB/scancode-toolkit/pull/2961/files and I'm guessing that broke this. I'm happy to work on a fix for this if this project is still under development and will accept PRs