Returns a symmetrically padded domain for polar charts
@param {Array} domain: the original domain
@param {Array} values: a flat array of values corresponding to either tickValues, or data values
for a given dimension i.e. only x values.
@returns {Array} the symmetric domain
function getSymmetricDomain(domain, values) {
  const processedData = sortedUniq(values.sort((a, b) => a - b));
  const step = processedData[1] - processedData[0];
  return [domain[0], domain[1] + step];
}