Multiple contributors detected as single author

### Description

For the [asaskevich/govalidator/README.md](https://github.com/asaskevich/govalidator/blob/3dd3875e2b081a20d6eed935913a482fea14ecd0/README.md) file ScanCode multiple contributors defined at the end of the file as a single author. It's also dropping the last author on the list.

### How To Reproduce

The following:

```
$ wget https://raw.githubusercontent.com/asaskevich/govalidator/3dd3875e2b081a20d6eed935913a482fea14ecd0/README.md
$ scancode --copyright --json result.json README.md
$ cat result.json | jq ".files"
```

Produces:

```
[
{
"path": "README.md",
"type": "file",
"copyrights": [],
"holders": [],
"authors": [
{
"author": "(https://github.com/asaskevich/govalidator/graphs/contributors) Daniel Lohse (https://github.com/annismckenzie) Attila Olah (https://github.com/attilaolah) Daniel Korner (https://github.com/Dadie) Steven Wilkin (https://github.com/stevenwilkin) Deiwin Sarjas (https://github.com/deiwin) Noah Shibley (https://github.com/slugmobile) Nathan Davies (https://github.com/nathj07) Matt Sanford (https://github.com/mzsanford)",
"start_line": 587,
"end_line": 595
}
],
"scan_errors": []
}
]
```

### System configuration

* What OS are you running on? (Windows/MacOS/Linux)
* Linux
* What version of scancode-toolkit was used to generate the scan file?
* `v33.0.0rc1-811-g4e8d711499`
* What installation method was used to install/run scancode? (pip/source download/other)
* Source download