(#18) Fix ignore of untested packages in coverage check

[llorllale]

PR for #18:

• No longer ignoring untested packages in coverage check
• Inserted exception for this package: github.com/llorllale/go-gitlint/cmd/go-gitlint

[codecov]

Codecov Report

Merging #19 into master will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff          @@
##           master   #19   +/-   ##
====================================
  Coverage      85%   85%           
====================================
  Files           4     4           
  Lines          80    80           
====================================
  Hits           68    68           
  Misses          6     6           
  Partials        6     6

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