refactor: simplify expression.

[zhangenming]

No description provided.

[zloirock]

Thanks, but in this case, we lose check of the existence of the passed method. Something like this:

uncurryThis(Array.prototype.groupBy); // => method or, if `groupBy` is not exist, `undefined`

[zloirock]

I don't think that it's a simplification - for many, the first line will seem even more confusing and this does not affect performance, however, let it be.