Add index on visits.create_time (#290)

Co-authored-by: Qianmian Yu <im.qianmian.yu@gmail.com>

eladmin-system/src/main/java/me/zhengjie/modules/monitor/domain/Visits.java

@@ -15,7 +15,8 @@ import java.sql.Timestamp;
  */
 @Entity
 @Data
-@Table(name = "visits")
+@Table(name = "visits",
+       indexes = {@Index(name = "visits_create_time_index", columnList = "create_time")})
 public class Visits  implements Serializable {
 
     @Id