fix typo in docs

[Hugo-Trentesaux]

fix typo

[codecov-io]

Codecov Report

Merging #1501 (9593d5c) into master (8954fe8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1501   +/-   ##
=======================================
  Coverage   89.62%   89.62%           
=======================================
  Files          39       39           
  Lines        4596     4596           
=======================================
  Hits         4119     4119           
  Misses        477      477           

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[bjarthur]

thanks!