config.go
func LoadJSON(conf interface{}, configPaths ...string) error {
	return loadWithFunc(conf, configPaths, nil, json.Unmarshal)
}
func LoadJSON(conf interface{}, configPaths ...string) error {
	return loadWithFunc(conf, configPaths, nil, json.Unmarshal)
}
// Load loads JSON files from `configPaths`.
// and assigns decoded values into the `conf` value.