Fix postgres drop fk

aerich/__init__.py

@@ -1 +1 @@
-__version__ = "0.2.1"
+__version__ = "0.2.2"

aerich/ddl/postgres/__init__.py

@@ -14,6 +14,7 @@ class PostgresDDL(BaseDDL):
     _ALTER_NULL_TEMPLATE = 'ALTER TABLE "{table_name}" ALTER COLUMN "{column}" {set_drop} NOT NULL'
     _MODIFY_COLUMN_TEMPLATE = 'ALTER TABLE "{table_name}" ALTER COLUMN "{column}" TYPE {datatype}'
     _SET_COMMENT_TEMPLATE = 'COMMENT ON COLUMN "{table_name}"."{column}" IS {comment}'
+    _DROP_FK_TEMPLATE = 'ALTER TABLE "{table_name}" DROP CONSTRAINT "{fk_name}"'
 
     def alter_column_default(self, model: "Type[Model]", field_object: Field):
         db_table = model._meta.db_table