Fix coverage path problem on Windows

[rly]

Fix #250

[codecov]

Codecov Report

Merging #251 into dev will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##              dev    #251      +/-   ##
=========================================
+ Coverage   70.29%   70.3%   +0.01%     
=========================================
  Files          33      33              
  Lines        5936    5938       +2     
  Branches     1393    1394       +1     
=========================================
+ Hits         4173    4175       +2     
  Misses       1328    1328              
  Partials      435     435

Impacted Files	Coverage Δ
src/hdmf/data_utils.py	90.8% <100%> (+0.06%)	⬆️

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