update readme

Author: Sung Kang

docs/terraform.md

@@ -57,7 +57,7 @@
 | port | Redis port | `number` | `6379` | no |
 | regex\_replace\_chars | Regex to replace chars with empty string in `namespace`, `environment`, `stage` and `name`.<br>If not set, `"/[^a-zA-Z0-9-]/"` is used to remove all characters other than hyphens, letters and digits. | `string` | `null` | no |
 | replication\_group\_id | Replication group ID with the following constraints: <br>A name must contain from 1 to 20 alphanumeric characters or hyphens. <br> The first character must be a letter. <br> A name cannot end with a hyphen or contain two consecutive hyphens. | `string` | `""` | no |
-| snapshot\_arns | (Optional) A single-element string list containing an Amazon Resource Name (ARN) of a Redis RDB snapshot file stored in Amazon S3. Example: arn:aws:s3:::my\_bucket/snapshot1.rdb | `list(string)` | `[]` | no |
+| snapshot\_arns | A single-element string list containing an Amazon Resource Name (ARN) of a Redis RDB snapshot file stored in Amazon S3. Example: arn:aws:s3:::my\_bucket/snapshot1.rdb | `list(string)` | `[]` | no |
 | snapshot\_name | The name of a snapshot from which to restore data into the new node group. Changing the snapshot\_name forces a new resource. | `string` | `null` | no |
 | snapshot\_retention\_limit | The number of days for which ElastiCache will retain automatic cache cluster snapshots before deleting them. | `number` | `0` | no |
 | snapshot\_window | The daily time range (in UTC) during which ElastiCache will begin taking a daily snapshot of your cache cluster. | `string` | `"06:30-07:30"` | no |