Use Object.defineProperty instead of __defineGetter__

[Pumpuli]

__defineGetter__ is non-standard and doesn't exist in IE<=10

[watson]

I don't see an issue with using Object.defineProperty, but there might be some compatibility issues with that one as well that I don't know of (it's ECMAScript 5 after all). Any particular reason you chose to use __defineGetter__ originally @mafintosh? If not, I think we can just merge this 😃 Or we could consider using a polyfill if compatibility is an issue

[Pumpuli]

Oh, I should've looked first. Now I see there's already #58, although that PR is mostly other parts and just removes the __defineGetter__ part completely. Also this doesn't apparently help IE8:

Object.defineProperty in Internet Explorer 8 only on DOM objects and with some non-standard behaviors.

https://mdn.io/defineProperty#Browser_compatibility

[Pumpuli]

Well, #100 was merged with the exact same change so this can be closed.