Returns the maxDomain from props if it exists
@param {Object} props: the props object
@param {String} axis: the current axis
@returns {Number|undefined} the maxDomain based on props
function getMaxFromProps(props, axis) {
  if (isPlainObject(props.maxDomain) && props.maxDomain[axis] !== undefined) {
    return props.maxDomain[axis];
  }
  return typeof props.maxDomain === "number" ? props.maxDomain : undefined;
}