Fix trivial typo in expressions.md

[MagicMuscleMan]

No description provided.

[blegat]

Thanks :)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.83%. Comparing base (f2fd118) to head (aeed49f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4093   +/-   ##
=======================================
  Coverage   99.83%   99.83%           
=======================================
  Files          43       43           
  Lines        5907     5907           
=======================================
  Hits         5897     5897           
  Misses         10       10           

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