Fix: Off-by-one Line/Column indexes from Hlint

[Arthi-chaud]

Hlint returns 1-indexed line and column numbers. However, nvim-lint uses indexes from 0. This causes Hlint's diagnostic to be reported on the wrong line/column

Example

Proof that Hlint reports 1-indexed line numbers

Here is the output of Hlint:

// hlint --json a.hs | jq
[
  {
    "module": [
      "Main"
    ],
    "decl": [
      "a"
    ],
    "severity": "Warning",
    "hint": "Redundant bracket",
    "file": "a.hs",
    "startLine": 1,
    "startColumn": 5,
    "endLine": 1,
    "endColumn": 8,
    "from": "(1)",
    "to": "1",
    "note": [],
    "refactorings": "[Replace {rtype = Expr, pos = SrcSpan {startLine = 1, startCol = 5, endLine = 1, endCol = 8}, subts = [(\"x\",SrcSpan {startLine = 1, startCol = 6, endLine = 1, endCol = 7})], orig = \"x\"}]"
  }
]

This PR fixes this issue and updates the tests accordingly.

Thanks for the plugin :)