Use String type for filePermission

[sushichop]

No description provided.

[codecov]

Codecov Report

Merging #43 (012e836) into main (788afe1) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #43   +/-   ##
=======================================
  Coverage   95.81%   95.81%           
=======================================
  Files          11       11           
  Lines         406      406           
=======================================
  Hits          389      389           
  Misses         17       17           

Impacted Files	Coverage Δ
Sources/Puppy/FileError.swift	100.00% <ø> (ø)
Sources/Puppy/FileLogger.swift	92.04% <100.00%> (ø)
Sources/Puppy/FileRotationLogger.swift	86.11% <100.00%> (ø)

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