Fix CDATA issue

[MaxDesiatov]

Resolves #168

[codecov]

Codecov Report

Merging #170 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #170      +/-   ##
==========================================
+ Coverage   72.84%   72.87%   +0.02%     
==========================================
  Files          43       43              
  Lines        2287     2289       +2     
==========================================
+ Hits         1666     1668       +2     
  Misses        621      621              

Impacted Files	Coverage Δ
Sources/XMLCoder/Auxiliaries/Box/KeyedBox.swift	100.00% <100.00%> (ø)
Sources/XMLCoder/Auxiliaries/KeyedStorage.swift	95.55% <100.00%> (+0.20%)	⬆️

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