Update docs in ProjectMetric class

[schalkms]

No description provided.

[codecov]

Codecov Report

Merging #2912 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2912   +/-   ##
=========================================
  Coverage     80.15%   80.15%           
  Complexity     2429     2429           
=========================================
  Files           421      421           
  Lines          7384     7384           
  Branches       1354     1354           
=========================================
  Hits           5919     5919           
  Misses          764      764           
  Partials        701      701           

Impacted Files	Coverage Δ	Complexity Δ
...n/io/gitlab/arturbosch/detekt/api/ProjectMetric.kt	80.00% <ø> (ø)	5.00 <0.00> (ø)

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