Alex Pernot

Replaced the deprecated **defineGetter**() with the standard Object.defineProperty(). Should now work with IE 9+ instead of 11+.

Hello, Arboreal crashes at loading at line 239 with IE 9. It seems __defineGetter__ [isn't standard and shouldn't be used at all](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/__defineGetter__). I'll try to submit a pull request later,...