fix(types): file appender types

[vdmtrv]

The Typescript types are wrong for the File appender. This is related to #807

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@f8d46a9). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1031   +/-   ##
=========================================
  Coverage          ?   98.46%           
=========================================
  Files             ?       25           
  Lines             ?     1040           
  Branches          ?        0           
=========================================
  Hits              ?     1024           
  Misses            ?       16           
  Partials          ?        0           

Impacted Files	Coverage Δ
lib/layouts.js	99.05% <0.00%> (ø)
lib/appenders/stderr.js	100.00% <0.00%> (ø)
lib/appenders/noLogFilter.js	100.00% <0.00%> (ø)
lib/appenders/console.js	100.00% <0.00%> (ø)
lib/levels.js	100.00% <0.00%> (ø)
lib/appenders/recording.js	100.00% <0.00%> (ø)
lib/logger.js	97.82% <0.00%> (ø)
lib/appenders/multiFile.js	94.11% <0.00%> (ø)
lib/appenders/tcp.js	91.30% <0.00%> (ø)
lib/appenders/categoryFilter.js	100.00% <0.00%> (ø)
... and 15 more

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