Upgrade the version of `timew-report`

[jonafato]

The version of timew-report was restricted in #10 to deal with failing tests. This change updates the version required by the Pipfile and makes the following code changes:

1. Update a test helper to pass in a value for the new required argument annotation. This is not used by the test suite, so the helper uses None for now.

2. Addresses some breaking changes and deprecation warnings in get_date released in 1.4. get_date now returns a date instead of a datetime. get_start_date offers the same implementation that get_date used to, so no logic has changed here, and this avoids deprecation warnings.

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Note that this pull request is branched from #13. These changes aren't actually related, but I wanted a stable testing state to base this upgrade on. The diff against master will be smaller once that other change is merged.