Fix files flag for windows

[g4s8]

• Enable Windows CI build
• Fix Windows file path separator

Fix: #43

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 71.38%. Comparing base (944acfd) to head (7d6f17f).

Files with missing lines	Patch %	Lines
ast/testhelper.go	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #47      +/-   ##
==========================================
- Coverage   71.53%   71.38%   -0.15%     
==========================================
  Files          32       32              
  Lines        1061     1066       +5     
==========================================
+ Hits          759      761       +2     
- Misses        261      263       +2     
- Partials       41       42       +1     

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