collecting owners from pacakge.contributors and pacakge.author if present.

[gagoar]

This PR provides support for contributors and author when using the flag --useMaintainers

fixes #21

[codecov]

Codecov Report

Merging #32 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #32   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          194       197    +3     
  Branches        29        30    +1     
=========================================
+ Hits           194       197    +3     

Flag	Coverage Δ
#unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/utils/codeowners.ts	100.00% <100.00%> (ø)

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