Fix syntax error in cookbook example

[offa]

There's a ; missing in the example.

[codecov[bot]]

Codecov Report

Merging #292 (7ce938f) into main (33af450) will increase coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #292      +/-   ##
==========================================
+ Coverage   97.95%   98.01%   +0.06%     
==========================================
  Files           1        1              
  Lines        1320     1312       -8     
==========================================
- Hits         1293     1286       -7     
+ Misses         27       26       -1     

Impacted Files	Coverage Δ
include/trompeloeil.hpp	98.01% <0.00%> (+0.06%)	:arrow_up:

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