Add reward to Captive unit

[olistic]

This was necessary to properly close #64.

[codecov-io]

Codecov Report

Merging #90 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #90   +/-   ##
======================================
  Coverage    90.4%   90.4%           
======================================
  Files          80      80           
  Lines        1011    1011           
  Branches      154     154           
======================================
  Hits          914     914           
  Misses         82      82           
  Partials       15      15

Impacted Files	Coverage Δ
packages/warriorjs-core/src/Unit.js	100% <ø> (ø)	⬆️
packages/warriorjs-core/src/LevelLoader.js	91.3% <ø> (ø)	⬆️
packages/warriorjs-units/src/Captive.js	100% <ø> (ø)	⬆️

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