refactor: use variable for environment prefix

cmd/client/client.go

@@ -11,14 +11,16 @@ import (
 	"go.uber.org/zap"
 )
 
+var envPrefix = "GOINV_CLI_"
+
 func main() {
 	logger, _ := zap.NewProduction()
 	defer logger.Sync()
 
 	config.LoadConfig(file.Provider("config.json"), json.Parser())
-	config.LoadConfig(env.Provider("GOINV_CLI_", ".", func(s string) string {
+	config.LoadConfig(env.Provider(envPrefix, ".", func(s string) string {
 		return strings.Replace(strings.ToLower(
-			strings.TrimPrefix(s, "GOINV_CLI_")), "_", ".", -1,
+			strings.TrimPrefix(s, envPrefix)), "_", ".", -1,
 		)
 	}), nil)