func LoadConfig(path, envPrefix string, config interface{}) error {
	if path != "" {
		err := LoadFile(path, config)
		if err != nil {
			return errors.Wrap(err, "error loading config from file")
		}
	}
	err := envconfig.Process(envPrefix, config)
	return errors.Wrap(err, "error loading config from env")
}
LoadConfig will load files optionally from the json file stored
at path, then will override those values based on the envconfig
struct tags. The envPrefix is how we prefix our environment
variables.
package envvar
import (
	"encoding/json"
	"os"
	"github.com/kelseyhightower/envconfig"
	"github.com/pkg/errors"
)