apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/ReleaseService.java/ReleaseService/mergeConfiguration
class ReleaseService:  private Map<String, String> mergeConfiguration(Map<String, String> baseConfigurations,
                                                 Map<String, String> coverConfigurations) {
    Map<String, String> result = new LinkedHashMap<>();
    //copy base configuration
    for (Map.Entry<String, String> entry : baseConfigurations.entrySet()) {
      result.put(entry.getKey(), entry.getValue());
    }

    //update and publish
    for (Map.Entry<String, String> entry : coverConfigurations.entrySet()) {
      result.put(entry.getKey(), entry.getValue());
    }

    return result;
  }