[Docs] Update hex.md

[KazukiOhta]

Did you mean player_id instead of player_ix?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.27%. Comparing base (3ad1677) to head (2c644a1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1285      +/-   ##
==========================================
- Coverage   80.29%   80.27%   -0.03%     
==========================================
  Files          62       62              
  Lines        5888     5885       -3     
==========================================
- Hits         4728     4724       -4     
- Misses       1160     1161       +1     

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[sotetsuk]

Correct! Thank you again for your PR!! 🙏