Update project bootstrap to v3.3.1

libgrabber updated project bootstrap to v3.3.1.

@twbs

### Metadata information

```json
{
  "metadata": {
    "packageManager": "github",
    "name": "bootstrap",
    "repo": "twbs/bootstrap",
    "files": {
      "basePath": "dist/",
      "include": ["**/*"],
      "exclude": []
    },
    "path": "/home/jsdelivr/files/bootstrap",
    "localVersions": ["2.0.4", "2.1.0", "2.1.1", "2.2.1", "2.2.2", "2.3.0", "2.3.1", "2.3.2", "3.0.0-rc1", "3.0.0-rc2", "3.0.0", "3.0.1", "3.0.2", "3.0.3", "3.1.0", "3.1.1", "3.2.0", "3.3.0"],
    "remoteVersions": ["v1.0.0", "v1.1.0", "v1.1.1", "v1.2.0", "v1.3.0", "v1.4.0", "v2.0.0", "v2.0.1", "v2.0.2", "v2.0.3", "v2.0.4", "v2.1.0", "v2.1.1", "v2.2.0", "v2.2.1", "v2.2.2", "v2.3.0", "v2.3.1", "v2.3.2", "v3.0.0-rc.2", "v3.0.0-rc1", "v3.0.0", "v3.0.1", "v3.0.2", "v3.0.3", "v3.1.0", "v3.1.1", "v3.2.0", "v3.3.0", "v3.3.1"],
    "branchVersions": []
  },
  "version": "v3.3.1",
  "updated": true,
  "updatePath": "/home/jsdelivr/files/bootstrap/3.3.1",
  "branch": "bootstrap/v3.3.1"
}
```