function getTranslation(out, mat) {
  out[0] = mat[12];
  out[1] = mat[13];
  out[2] = mat[14];

  return out;
}
Returns the translation vector component of a transformation
 matrix. If a matrix is built with fromRotationTranslation,
 the returned vector will be the same as the translation vector
 originally supplied.
@param  {vec3} out Vector to receive translation component
@param  {mat4} mat Matrix to be decomposed (input)
@return {vec3} out