[BUG] Multiple Y-Axes example in README seems to be outdated

[SvHu]

Describe the bug
When adding example data to application to produce multiple Y-Axes then it does not work and produces error undefined method 'first' for 1.4:Float

To Reproduce
Steps to reproduce the behavior:

1. copy code to your app
2. visit page

Expected behavior
Should see same chart as given in readme file

Additional context
And even if I do something like this, then the opposite yaxis still wont appear

series = [
        {
          name: 'Income',
          type: 'column',
          data: {2009 => 1.1, 2010 => 2, 2011=>2.5, 2012=>1.5}
          #[1.4, 2, 2.5, 1.5, 2.5, 2.8, 3.8, 4.6]
        },
        {
          name: 'Cashflow',
          type: 'column',
          data: {2009 => 1.1, 2010=> 2, 2011=>3.17, 2012=>4}
          #[1.1, 3, 3.1, 4, 4.1, 4.9, 6.5, 8.5]
        },
        {
          name: 'Revenue',
          data: {2009 => 20, 2010=> 29, 2011=>37, 2012=>36}
          #[20, 29, 37, 36, 44, 45, 50, 58]
        }
      ]

      xaxis = {
        title: {text: 'Year'},
        categories: [2009, 2010, 2011, 2012]
      }

      yaxis = [
        {title: {text: "Income"}},
        {
          title: {text: "Operating Cashflow"},
          opposite: true,
          seriesName: 'Cashflow'
        },
        {
          title: {text: "Revenue"},
          opposite: true,
          seriesName: 'Revenue'
        }
      ]
      line_chart(series, xaxis: xaxis, yaxis: yaxis, defer: true)

It would be nice if there would be actually example for combo_chart chart also

[SvHu]

Oh, I just noticed that actually these changes are still only in master branch and not in any latest version. Also FYI version 1.11.0 needs try schema version which requires ruby 2.6.0. I'm using ruby 2.5 so that is at least blocked also for me. Please update the gem requirements.