Switched default API version for JWT
Switched default API version for JWT

refs https://github.com/TryGhost/Ghost/issues/12716

- This change is made to avoid using now deprecated 'v2' API anywhere in the codebase.
- Switching to 'v4' should not cause sideeffects as this parameter is always present within the URL when Admin API is used

e10/Ghost,bitjson/Ghost,ErisDS/Ghost,ErisDS/Ghost,ErisDS/Ghost,TryGhost/Ghost,e10/Ghost,TryGhost/Ghost,janvt/Ghost,janvt/Ghost,bitjson/Ghost,TryGhost/Ghost