Add testcase to test deletion to fix #44

[maikelpoot]

This PR will add a test case that touches deletions within apply.

Tested this also with the "old" code and it did catch the runtime error:

% ./script/test
...
        for change in changes:
            record = change.new

>           if record.name == '' and record._type == 'NS':
E           AttributeError: 'NoneType' object has no attribute 'name'

octodns_transip/__init__.py:259: AttributeError
...
=== short test summary info ===
FAILED tests/test_provider_octodns_transip.py::TestTransipProvider::test_apply_deletions - AttributeError: 'NoneType' object has no attribute 'name'
=== 1 failed, 21 passed in 0.35s