pass keys to lume.map function

[solarized-fox]

I'm currently in the process of swapping my home-brewed util library for lume. one sticking point is that my version of map passes the value and key to the mapper function, which means I have to modify lume a bit. it should be as simple as changing rtn[k] = f(v) to rtn[k] = f(v, k). I seriously doubt that this would break any existing code (aren't dynamic function arities wonderful?) so if folks think it's a good idea I can make a pull request for this, might also propagate this change to some of the other higher order functions like filter while I'm at it