I tried to use GeoChart but it did not initiate. I further investigate and find that geochart library is not loaded before it inits. I fixed it by changing the addScriptOnEnd() to addScriptOnBegin() and it works.
$this->getReport()->getResourceManager()
->addScriptOnBegin("google.charts.load('current', {'packages':['geochart']})");
Please apply this change to the next version.