playhouse.reflection.generate_models reorders compound index keys
Verified on Postgres 12 as well. Thanks for the report. Fixed. Thanks again for the report!
Using peewee 3.13.1 with PostgreSQL 9.6.15 and psycopg2 2.8.2, I noticed that a model class generated with `generate_models()` had the incorrect order for the keys of a reflected compound index:

```
# \d typicaluser
                              Table "public.typicaluser"
   Column   |  Type   | Collation | Nullable |                 Default
------------+---------+-----------+----------+-----------------------------------------
 id         | integer |           | not null | nextval('typicaluser_id_seq'::regclass)
 first_name | text    |           | not null |
 last_name  | text    |           | not null |
 email      | text    |           | not null |
Indexes:
    "typicaluser_pkey" PRIMARY KEY, btree (id)
    "typicaluser_last_name_first_name" btree (last_name, first_name)
```

vs. 

```
>>> from playhouse.reflection import generate_models
>>> models = generate_models(database)
>>> models["typicaluser"]._meta.indexes
[(['first_name', 'last_name'], False)]
```

Note that the generated model has `['first_name', 'last_name']` vs the `(last_name, first_name)` order in the database.