Fix a typo in the documentation

[martin-cs]

Fixes #5805

[martin-cs]

@tautschnig : pretty sure that the CSmith failure is unrelated, any chance you could take a look

https://github.com/diffblue/cbmc/actions/runs/549356384

[codecov]

Codecov Report

Merging #5806 (4efe207) into develop (441a249) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5806   +/-   ##
========================================
  Coverage    69.72%   69.72%           
========================================
  Files         1242     1242           
  Lines       100907   100907           
========================================
  Hits         70361    70361           
  Misses       30546    30546           

Flag	Coverage Δ
cproversmt2	43.38% <ø> (ø)
regression	66.69% <ø> (ø)
unit	32.29% <ø> (ø)

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[tautschnig]

@tautschnig : pretty sure that the CSmith failure is unrelated, any chance you could take a look

https://github.com/diffblue/cbmc/actions/runs/549356384

Yes, sorry, that would be fixed by #5799.