Fix **self._kwargs

[mrakitin]

Discovered today while working on NSLS-II-QAS/profile_collection#30.

[mrakitin]

@tacaswell, we discovered the issue while trying to pass the metadata to TiffWriter.write(). Do you happen to know how to format the metadata properly? We tried the following, but it did not work:

        metadata={"imagej_metadata_tag": {
            "Info": datetime.datetime.now().isoformat()
            }
        }

[mrakitin]

=========================== short test summary info ============================
FAILED suitcase/tiff_series/tests/tests.py::test_2d_data[False] - KeyError: 'stream_data'
FAILED suitcase/tiff_series/tests/tests.py::test_2d_data[True] - KeyError: 'stream_data'
FAILED suitcase/tiff_series/tests/tests.py::test_3d_data[False] - KeyError: 'stream_data'
FAILED suitcase/tiff_series/tests/tests.py::test_3d_data[True] - KeyError: 'stream_data'
FAILED suitcase/tiff_series/tests/tests.py::test_2d_data_lies[False] - Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) were emitted.
The list of emitted warnings is: [].
FAILED suitcase/tiff_series/tests/tests.py::test_2d_data_lies[True] - Failed: DID NOT WARN. No warnings of type (<class 'Warning'>,) were emitted.
The list of emitted warnings is: [].
================= 6 failed, 724 passed, 240 warnings in 9.40s ==================