[baseline output] Add sort_keys=True to json.dumps

[KevinHock]

This prevents unnecessary baseline modifications where the pre-commit hook can change the baseline only to re-order keys around (on certain python versions.)

Note that this will make it read differently then before, but in my opinion it's even more readable as the exclude_regex is no longer at the bottom after the results.

With sort_keys it is e.g.

{
  "exclude_regex": null,
  "generated_at": "2018-06-14T20:55:58Z",
  "plugins_used": [
    {
      "limit": 4.5,
      "name": "Base64HighEntropyString"
    },
    {
      "limit": 3,
      "name": "HexHighEntropyString"
    },
    {
      "name": "PrivateKeyDetector"
    }
  ],
  "results": {
    "test_data/baseline.file": [
      {
        "hashed_secret": "fdd121830f7c0a035298a08a79c7a34835184b8a",
        "line_number": 9,
        "type": "High Entropy String"
      },
      {
....
  },
  "exclude_regex": null
}

Whereas without sort_keys it is e.g.

  "plugins_used": [
    {
      "limit": 4.5,
      "name": "Base64HighEntropyString"
    },
    {
      "limit": 3,
      "name": "HexHighEntropyString"
    },
    {
      "name": "PrivateKeyDetector"
    }
  ],
  "generated_at": "2018-06-14T20:55:23Z",
  "results": {
    "tests/pre_commit_hook_test.py": [
      {
        "line_number": 154,
....
  },
  "exclude_regex": null
}

[domanchi]

You probably want to do it in other places too.

E.g. https://github.com/Yelp/detect-secrets/blob/master/detect_secrets/pre_commit_hook.py#L57

[KevinHock]

Great catch!