fix: search_entities default "format" value is invalid
fix: search_entities default "format" value is invalid

The example given in readme doesn't work, this should fix it.

Url generated : https://www.wikidata.org/w/api.php?action=wbsearchentities&search=Ingmar%20Bergman&language=fr&limit=10&format=20

Error returned :
```
"error": {
        "code": "unknown_format",
        "info": "Unrecognized value for parameter 'format': 20",
        "*": "See https://www.wikidata.org/w/api.php for API usage"
    }
```
maxlath/wikidata-sdk,maxlath/wikidata-sdk,maxlath/wikidata-sdk