Use explicit date for test expectation

Makes it clearer what is being tested for.
Format json timestamps without time offset

This reflects what is actually being returned because of DataMapper
killing time offsets.
The time offsets will come back when the DataMapper patch goes in and
the data is migrated.
Merge pull request #4 from alphagov/use-explicit-dates

Use explicit date for test expectation
Merge pull request #5 from alphagov/remove-timezone-in-json

Format json timestamps without time offset