Update OpenAPI specification

[soskape]

• the endpoint '/payments/{transactionId}/token/commit' does not contain 'transactionId' path parameter definition
• the endpoint '/payments/{transactionId}/token/revert' does not contain 'transactionId' path parameter definition
• the Payment object attributes stamp and reference are in wrong order - first is 'stamp' then 'reference', but response and also the hmac calculation is calculated from the object with first 'reference' and then 'stamp'.
• the open api version is '3.0.0' instead of 3.0.0

Maybe I will find more during the implementation...

[jfrojd-paytrail]

Thank you for the notes, we'll have a look and implement necessary fixes.