fix missing arg name in option-pricing example

[slayoo]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.93%. Comparing base (c37a0fa) to head (2016079).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #648   +/-   ##
=======================================
  Coverage   92.93%   92.93%           
=======================================
  Files          40       40           
  Lines        1754     1754           
=======================================
  Hits         1630     1630           
  Misses        124      124           

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