Google visualization graphs code giving me problem

this code giving me error " google is not defined "
Any idea please to implement it

 <template name="home">
<html>
<head>
<script type="text/javascript" src="https://www.google.com/jsapi"></script>
<script type="text/javascript">

google.load(‘visualization’, ‘1.0’, {‘packages’:[‘corechart’]});

// Set a callback to run when the Google Visualization API is loaded.
google.setOnLoadCallback(drawChart);

// Callback that creates and populates a data table,
// instantiates the pie chart, passes in the data and
// draws it.
function drawChart() {

// Create the data table.
var data = new google.visualization.DataTable();
data.addColumn('string', 'Topping');
data.addColumn('number', 'Slices');
data.addRows([

[‘Mushrooms’, 3],
[‘Onions’, 1],
[‘Olives’, 1],
[‘Zucchini’, 1],
[‘Pepperoni’, 2]
]);

// Set chart options
var options = {'title':'How Much Pizza I Ate Last Night',

‘width’:400,
‘height’:300};

// Instantiate and draw our chart, passing in some options.
var chart = new google.visualization.PieChart(document.getElementById('chart_div'));
chart.draw(data, options);

}

<body>
<!--Div that will hold the pie chart-->
<div id="chart_div"></div>
</body>
</html>