fix typo

Signed-off-by: Ruihang Xia <waynestxia@gmail.com>

docs/nightly/en/user-guide/continuous-aggregation/manage-flow.md

@@ -27,7 +27,7 @@ When `OR REPLACE` is specified, if a flow with the same name already exists, it
 
 `sink-table-name` is the table name to store the materialized aggregated data. It can be an existing table or a new table, `flow` will create the sink table if it doesn't exist. But if the table already exists, the schema of the table must match the schema of the query result.
 
-`expire after` is an optional inverval to expire the data from the source table. The expiration time is a relative time from the current time (by "current time" we means the physical time of the data arrive the Flow engine). For example, `INTERVAL '1 hour'` means the data after 1 hour from the current time will be expired. Expired will be dropped directly.
+`expire after` is an optional interval to expire the data from the source table. The expiration time is a relative time from the current time (by "current time" we means the physical time of the data arrive the Flow engine). For example, `INTERVAL '1 hour'` means the data after 1 hour from the current time will be expired. Expired will be dropped directly.
 
 `SQL` part defines the continuous aggregation query. Refer to [Query](./query.md) for the details. Generally speaking, the `SQL` part is just like a normal `SELECT` clause with a few difference.