fix(ica): add missing exponential

[lmmx]

• Via [linfa-ica] GFunc::Exp computes incorrect g and g' derivatives #425

Simple fix to the exp variant of fast ICA algo, a missing .exp() call

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.00%. Comparing base (9b5c424) to head (681da88).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #426   +/-   ##
=======================================
  Coverage   77.00%   77.00%           
=======================================
  Files         106      106           
  Lines        7461     7461           
=======================================
  Hits         5745     5745           
  Misses       1716     1716           

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