bump zarr with support for dimension_separator

[manzt]

@will-moore @joshmoore

Zarr.js now has support for dimension_separator, so the store should no long need to modify chunk keys. It would be my preference that we rely on zarr rather than inspecting the ome metadata to determine how to initialize a custom store.

It is my impression that datasets coming from the IDR (or generated with bioformats2raw) will include dimension_separator in the array metadata.

[joshmoore]

Speaking for the Python & Java implementations, the ome-zarr v0.2+ implementations should explicitly pass / which should trigger the zarr implementations to set dimension_separator in the metadata, so that sounds like a fair assumption.

[will-moore]

This is working great for me, with the sample data from #103 and other data I've created locally.
I'm adding more to #104 just now, so once this is merged I can fix conflicts etc. Thanks.

[manzt]

Ok great, merging!