update SQL Server flyway migrations

[mattStorer]

MU is encountering an issue in flyway migrations that is due to the alter table syntax not being correct.

looks like this:

alter table home_pulse_reading modify source varchar(10) not null;

needs to be this:

alter table home_pulse_reading alter column source varchar(10) not null;

[mattStorer]

tested these migrations in a SQL server environment as they would be executed by Flyway, and everything went through fine.