[sql-hint addon] Add tests and fix #5817

[williamdes]

• [sql-hint addon] Add tests for defaultTable and disableKeywords
• [sql-hint addon] Fix [regression] Hint displays '[object]' #5817

[williamdes]

You can see in https://travis-ci.org/codemirror/CodeMirror/builds/508598677#L491 that the object is wraped in an object, this is the issue #5819

{
    "text": {
        "text": "alias",
        "displayText": "alias | varchar(255) | Primary",
        "columnName": "alias",
        "columnHint": "varchar(255) | Primary"
    },
    "className": "CodeMirror-hint-table CodeMirror-hint-default-table"
}

MUST be

{
  "text": "alias",
  "displayText": "alias | varchar(255) | Primary",
  "columnName": "alias",
  "columnHint": "varchar(255) | Primary",
  "className": "CodeMirror-hint-table CodeMirror-hint-default-table"
}

[marijnh]

Thanks!