Fix NaNMath usage example in README

[devmotion]

Fixes #97

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.15%. Comparing base (b1040f3) to head (9365d13).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #99   +/-   ##
=======================================
  Coverage   94.15%   94.15%           
=======================================
  Files           1        1           
  Lines         154      154           
=======================================
  Hits          145      145           
  Misses          9        9           

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