Change v2 files to v1
Adjust leap year birthday forward by one day

- For birthdays which fall on the 29th February in a leap year the calculator shifts their birthday to the 1st March for the purposes of finding the correct rate.
- This is similar to what the calculate-state-pension tool does.
Merge pull request #1153 from alphagov/fix-errbit-error-state-pension-topup

Fix errbit error state pension topup