[visualization-api] How do I make two y-axis's baseline same line in combo chart?

['Ziming Wang' via Google Visualization API]

As the screenshot shown, two baseline are two different lines. How can I 
make them same line in combo chart? Thanks!
Here is the chart's option: 

options={{
  pointsVisible: true,
  vAxes: {
    0: { format: 'decimal', baselineColor: 'red' },
    1: { format: 'percent', baselineColor: 'blue' },
  }​,
  series: {
    0: { type: 'bars', targetAxisIndex: 0 },
    1: { type: 'line', targetAxisIndex: 1 },
  },
}}

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