code: function monthConfigs () {
    return [
      [{
        interval: Plottable.TimeInterval.month,
        step: 1,
        // full month name
        formatter: Plottable.Formatters.time('%B')
      }, {
        interval: Plottable.TimeInterval.year,
        step: 1,
        formatter: Plottable.Formatters.time('%Y')
      }],
      [{
        interval: Plottable.TimeInterval.month,
        step: 1,
        // short month name
        formatter: Plottable.Formatters.time('%b')
      }, {
        interval: Plottable.TimeInterval.year,
        step: 1,
        formatter: Plottable.Formatters.time('%Y')
      }],
      [{
        interval: Plottable.TimeInterval.month,
        step: 1,
        // month in numbers
        formatter: Plottable.Formatters.time('%m')
      }, {
        interval: Plottable.TimeInterval.year,
        step: 1,
        formatter: Plottable.Formatters.time('%Y')
      }],
      [{
        interval: Plottable.TimeInterval.month,
        step: 1,
        // month in numbers
        formatter: Plottable.Formatters.time('%-m')
      }, {
        interval: Plottable.TimeInterval.year,
        step: 1,
        formatter: Plottable.Formatters.time('%Y')
      }]
    ]
  }
docs: use the month steps in the orginal plottable library