Upgrade to Flyway 7.1.1

[snicoll]

[wilkinsona]

Unfortunately this needs to be reverted due to flyway/flyway#2991.

[wilkinsona]

With thanks to @MikielAgutu and @DoodleBobBuffPants for the lightning-fast turnaround, Flyway 7.1.1 is out with a fix for flyway/flyway#2991 so we can have another go at this one.