code: function(projectConfig, variationId) {
      if (projectConfig.variationIdMap.hasOwnProperty(variationId)) {
        return projectConfig.variationIdMap[variationId].key;
      }
      return null;
    }
docs: Get variation key given experiment key and variation ID
  @param  {Object} projectConfig Object representing project configuration
  @param  {string} variationId   ID of the variation
  @return {string} Variation key or null if the variation ID is not found