key column length (256 chars) makes problem in long key rate limitation in postgres 
The `key` column in the generated table by `RateLimiterPostgres` is defined in this way:

```
character varying (256)
```

So when the length of selected key is bigger than 256 characters, it fails, without any log and just returns 429!!! 

I've used SHA-256 hash function to create 256 characters-key to make sure that it never fails