classNames, cellClassNames cannot be arrays

[buschtoens]

https://github.com/offirgolan/ember-light-table/blob/v1.8.6/addon/classes/Column.js#L259-L265

  /**
   * Class names to be applied to all cells of this column
   *
   * @property cellClassNames
   * @type {String | Array}
   */
  cellClassNames: null,

https://github.com/offirgolan/ember-light-table/blob/v1.8.6/addon/components/cells/base.js#L15-L25

/**
 * @module Cell Types
 * @class Base Cell
 */

const Cell = Component.extend({
  layout,
  tagName: 'td',
  classNames: ['lt-cell'],
  attributeBindings: ['style'],
  classNameBindings: ['align', 'isSorted', 'column.cellClassNames'],
  // ..
});

The same goes for classNames.

When passed an array of class names, the array is stringified (concatenated with ,).

I'll submit a PR when I can get around to it. Merely putting this here for tracking. 🙂
Otherwise this would be a great PR for a first-time contributor! 😄