Bump schema-ddl to 0.15.2

[istreeter]

Schema-ddl 0.15.2 has an important fix for Redshift.

For example, the Snowplow site_search schema has a field like this:

    "filters": {
      "type": "object",
      "additionalProperties": {
        "type": [
          "string",
          "boolean"
        ]
      }
    },

Before this fix, schema-ddl would yield two different columns called filters in the DDL:

 "filters"        VARCHAR(1024)  ENCODE ZSTD,                                                                                                                                                                                                                     
 "filters"        VARCHAR(4096)  ENCODE ZSTD, 

RDB loader would fail with a message like:

[Amazon](500310) Invalid operation: column "filters" duplicated; - SqlState: 42701