Update project momentjs to 2.8.1

libgrabber updated project momentjs to 2.8.1.

@moment

### Metadata information

```json
{
  "metadata": {
    "packageManager": "github",
    "name": "momentjs",
    "repo": "moment/moment",
    "files": {
      "basePath": "min/",
      "include": ["**/*"],
      "exclude": []
    },
    "path": "/home/jsdelivr/files/momentjs",
    "localVersions": ["1.7.2", "2.0.0", "2.1.0", "2.2.1", "2.3.1", "2.4.0", "2.5.0", "2.5.1", "2.6.0", "2.7.0"],
    "remoteVersions": ["0.6.0", "0.6.1", "1.0.1", "1.1.0", "1.1.1", "1.1.2", "1.2.0", "1.3.0", "1.4.0", "1.5.0", "1.5.1", "1.6.0", "1.6.1", "1.6.2", "1.7.0", "1.7.1", "1.7.2", "2.0.0", "2.1.0", "2.2.0", "2.2.1", "2.3.0", "2.3.1", "2.4.0", "2.5.0", "2.5.1", "2.6.0", "2.7.0", "2.8.0", "2.8.1"],
    "branchVersions": []
  },
  "version": "2.8.1",
  "updated": true,
  "updatePath": "/home/jsdelivr/files/momentjs/2.8.1",
  "branch": "momentjs/2.8.1"
}
```