Update scoredist implementation

[miccolis]

The scoredist method claims to be equivalient of the method of the same name in carmen, but it really is not.

• scoredist in carmen-cache

  carmen-cache/src/cpp_util.cpp

  Lines 111 to 123 in fd7398e

  	double scoredist(unsigned zoom, double distance, double score, double radius) {
  	if (zoom < 6) zoom = 6;
  	if (distance == 0.0) distance = 0.01;
  	double scoredist = 0;
  	// Since distance is in tiles we calculate scoredist by converting the miles into
  	// a tile unit value at the appropriate zoom first.
  	//
  	// 32 tiles is about 40 miles at z14, use this as our mile <=> tile conversion.
  	scoredist = ((radius * (32.0 / 40.0)) / _pow(1.5, 14 - static_cast<int>(zoom))) / distance;
  	return score > scoredist ? score : scoredist;
  	}

• scoredist in carmen https://github.com/mapbox/carmen/blob/f831f2dfc9eb965752939f5809b18315b38b7659/lib/util/proximity.js#L81-L90

We should most likely update the version here to actually be equivalent of what is over in carmen.