Safari window.crypto.webkitSubtle support?

I notice in https://github.com/nvdbleek/web-crypto-samples/blob/master/js/utils.js you don't look for the Safari window.crypto.webkitSubtle object - is there a specific reason Safari is excluded?

That's not a complaint BTW - only reason I'm asking is I'm working on my own code and Safari seems to have off problems like .exportKey() never resolving. 
