Update tags to be lowercase

[mtmk]

fixes #37

[codecov]

Codecov Report

Attention: Patch coverage is 92.10526% with 6 lines in your changes missing coverage. Please review.

Project coverage is 80.64%. Comparing base (e003239) to head (43a8581).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/NATS.Jwt/Models/NatsTags.cs	87.50%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #38      +/-   ##
==========================================
+ Coverage   79.73%   80.64%   +0.91%     
==========================================
  Files          49       51       +2     
  Lines         893      966      +73     
  Branches       81       92      +11     
==========================================
+ Hits          712      779      +67     
- Misses        155      160       +5     
- Partials       26       27       +1     

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[caleblloyd]

Nice! LGTM