You need to update your HTTP headers to accept v5
Accept: application/vnd.twitchtv.v5+json
Your client ID should also be an HTTP header, not a query string.
e.g.
curl -H 'Accept: application/vnd.twitchtv.v5+json' \
-H 'Client-ID: uo6dggojyb8d6soh92zknwmi5ej1q2' \
-X GET 'https://api.twitch.tv/kraken/streams/?game=Overwatch'