失敗時のSL0表示を+0から-0に修正

[Faceless192x]

WHコマンドの成功度判定について、失敗時にSLが0だったときルール上は「-0」表記しなくてはいけないが「+0」表記になっていた不具合の修正。

bundle exec rake test:dicebots target=Warhammer4　実行済み。

[codecov]

Codecov Report

Base: 95.40% // Head: 95.40% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (1e70004) compared to base (71532d4).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #585   +/-   ##
=======================================
  Coverage   95.40%   95.40%           
=======================================
  Files         324      324           
  Lines       18296    18298    +2     
  Branches     4741     4743    +2     
=======================================
+ Hits        17456    17458    +2     
  Misses        840      840           

Impacted Files	Coverage Δ
lib/bcdice/game_system/Warhammer4.rb	96.19% <100.00%> (+0.07%)	⬆️

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[ysakasin]

@Faceless192x ありがとうございます。マージしました。

[Faceless192x]

ありがとうございます！