Fix #33 and another netcdf-related bug

[meggart]

This fixes #33 and another bug which led to an error when trying to save a cube that had non-standard string types (like Zarr.MaxLengthString) in it axes. I can't remember the issue right now, a hint by @noralinscheid or @felixcremer would be great

[codecov]

Codecov Report

Merging #57 (e3f50a8) into master (107996c) will increase coverage by 0.44%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
+ Coverage   55.12%   55.56%   +0.44%     
==========================================
  Files          13       13              
  Lines        1531     1544      +13     
==========================================
+ Hits          844      858      +14     
+ Misses        687      686       -1     

Impacted Files	Coverage Δ
src/DatasetAPI/Datasets.jl	69.62% <93.33%> (+1.76%)	⬆️

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[coveralls]

Pull Request Test Coverage Report for Build 812832324

• 14 of 15 (93.33%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 55.476%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/DatasetAPI/Datasets.jl	14	15	93.33%

Files with Coverage Reduction	New Missed Lines	%
src/DatasetAPI/Datasets.jl	1	69.28%

Totals
Change from base Build 773593482:	0.3%
Covered Lines:	856
Relevant Lines:	1543

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💛 - Coveralls

[felixcremer]

This was in #23 here and issue 3 in YaxarrayBase.