You need to add a reference of the file called offline-exporting.js to make the client side exporting available. Please be noted this feature is not supported in browser IE 8, So if you load this chart in any unsupported browser, the module will fall back to the export server. This can be handled with the option fallbackToExportServer: false. You need to set this option in your exporting settings as follows.
exporting: {
chartOptions: {
plotOptions: {
series: {
dataLabels: {
enabled: true
}
}
}
},
scale: 3,
fallbackToExportServer: false
}