Change angle index label from google chart

[Sterica Capatina]

I have this code from google chart

google.charts.load("current", {packages:['corechart']});
    google.charts.setOnLoadCallback(drawChart);
    function drawChart() {
      var data = google.visualization.arrayToDataTable([
        ["Element", "Density", { role: "style" } ],
        ["Copper", 8.94, "#b87333"],
        ["Silver", 10.49, "silver"],
        ["Gold", 19.30, "gold"],
        ["Platinum", 21.45, "color: #e5e4e2"]
      ]);

      var view = new google.visualization.DataView(data);
      view.setColumns([0, 1,
                       { calc: "stringify",
                         sourceColumn: 1,
                         type: "string",
                         role: "annotation" },
                       2]);

      var options = {
        title: "Density of Precious Metals, in g/cm^3",
        width: 600,
        height: 400,
        bar: {groupWidth: "95%"},
        legend: { position: "none" },
      };
      var chart = new 
google.visualization.ColumnChart(document.getElementById("columnchart_values"));
      chart.draw(view, options);
  }


How could I change the angle from horizontal to vertical for the values 
from the index label (8.94; 10.49, 19.3).
Rotate text from 0 to 90, that here: http://i.stack.imgur.com/qAtQj.png
Thank you!

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