Fixes head repo decode failure

[fedefernandez]

Please @juanpedromoreno, could you review? Thanks

[juanpedromoreno]

Changes look good to me! Thanks @fedefernandez

[juanpedromoreno]

👍

[codecov-io]

Codecov Report

Merging #100 into master will not change coverage.
The diff coverage is 83.33%.

@@           Coverage Diff           @@
##           master     #100   +/-   ##
=======================================
  Coverage   87.81%   87.81%           
=======================================
  Files          36       36           
  Lines         517      517           
  Branches        3        3           
=======================================
  Hits          454      454           
  Misses         63       63

Impacted Files	Coverage Δ
.../main/scala/github4s/free/domain/PullRequest.scala	100% <ø> (ø)	⬆️
...ub4s/shared/src/main/scala/github4s/Decoders.scala	96.47% <83.33%> (ø)	⬆️

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