fix: change the structure of aqua-checksums.json

[suzuki-shunsuke]

AS IS

{
  "checksums": {
    "github_archive/github.com/b3nj5m1n/xdg-ninja/v0.2.0.1": "f4f9ab4500e7cf865ff8b68c343537e27b9ff1e6068cb1387e516e608f77cec8"
  }
}

TO BE

{
  "checksums": [
    {
      "id": "github_archive/github.com/b3nj5m1n/xdg-ninja/v0.2.0.1",
      "checksum": "f4f9ab4500e7cf865ff8b68c343537e27b9ff1e6068cb1387e516e608f77cec8",
      "algorithm": "sha256"
    }
  ]
}

WHY

The current format doesn't have the checksum algorithm.
The current default checksum algorithm is sha512, but when this will be changed, the configuration file will be broken.
To solve the problem, the new format has the checksum algorithm.
Additionally, the value is not a atring but a object, so we can add new fields in future keeping the compatibility.