fix(windows): Fix path issues on Windows

[dpogue]

Xcode pbxproj files must always use POSIX-style paths internally

Closes #123.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.30%. Comparing base (ca3d1d2) to head (fc92e52).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #170   +/-   ##
=======================================
  Coverage   97.30%   97.30%           
=======================================
  Files          51       51           
  Lines       10928    10928           
=======================================
  Hits        10634    10634           
  Misses        294      294           

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