Fix JsonMatcher (parsing DateTimeOffset)

[StefH]

No description provided.

[codecov]

Codecov Report

Merging #358 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #358      +/-   ##
==========================================
+ Coverage    80.5%   80.53%   +0.02%     
==========================================
  Files         114      114              
  Lines        4566     4573       +7     
==========================================
+ Hits         3676     3683       +7     
  Misses        890      890

Impacted Files	Coverage Δ
src/WireMock.Net/Util/JsonUtils.cs	100% <100%> (ø)	⬆️
...rc/WireMock.Net/Transformers/HandleBarsJsonPath.cs	97.77% <100%> (ø)	⬆️
src/WireMock.Net/Matchers/JsonMatcher.cs	89.47% <100%> (ø)	⬆️

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