Fix Parsing Guid in PUT Mapping

[StefH]

No description provided.

[codecov]

Codecov Report

Merging #326 into master will increase coverage by 0.14%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #326      +/-   ##
==========================================
+ Coverage   79.93%   80.08%   +0.14%     
==========================================
  Files         111      111              
  Lines        4420     4423       +3     
==========================================
+ Hits         3533     3542       +9     
+ Misses        887      881       -6

Impacted Files	Coverage Δ
src/WireMock.Net/Server/FluentMockServer.Admin.cs	62.87% <50%> (+1.25%)	⬆️

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