The problem is most likely the version of html2canvas you used. html2canvas 0.4.1 is not going to work. It should be html2canvas 1.0.0-alpha.11 or higher. However, current version, html2canvas 1.0.0-rc.3 doesn't work either, it also gives me a blank page. At least html2canvas 1.0.0-alpha.12 still works for me.
Update: the latest version that works for me is html2canvas v1.0.0-rc.1