Fix isStringLiteral with unicode strings

[WebFreak001]

No description provided.

[codecov]

Codecov Report

Merging #472 (f6c55dd) into master (abeefa2) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #472      +/-   ##
==========================================
+ Coverage   83.16%   83.17%   +0.01%     
==========================================
  Files          11       11              
  Lines        8345     8350       +5     
==========================================
+ Hits         6940     6945       +5     
  Misses       1405     1405              

Impacted Files	Coverage Δ
src/dparse/strings.d	98.72% <100.00%> (+0.01%)	⬆️

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