The vaccine offsets seem not to work as expected

[ekigamba]

https://github.com/OpenSRP/opensrp-client-giz-malawi has MV 1 and MV 2 vaccines where MV 1 should be given 5 months after birth and MV 2 should be given 1 month after MV 1 was given with a window of 14 days.

To replicate

1. Create a child on the GIZ Malawi app with a DOB two years behind
2. Give the child the MV 1 vaccine with a date either 7 months, 4 months or 1 year from the DOB
3. Check the due date of the MV 2 vaccine

The due date for the MV 2 vaccine is always at 6 months from birth irrespective of the date MV 1 was given