docs(manual): fix typos in assocs manual

[gosuhiman]

This PR contains simple fixes of typos in assocs manual - Foo and Bar was switched by mistake.

[codecov]

Codecov Report

Merging #11888 into master will decrease coverage by 3.78%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #11888      +/-   ##
==========================================
- Coverage   96.27%   92.48%   -3.79%     
==========================================
  Files          94       91       -3     
  Lines        9209     8916     -293     
==========================================
- Hits         8866     8246     -620     
- Misses        343      670     +327

Impacted Files	Coverage Δ
lib/dialects/sqlite/query-generator.js	2.91% <0%> (-93.69%)	⬇️
lib/dialects/sqlite/query-interface.js	15.62% <0%> (-84.38%)	⬇️
lib/dialects/sqlite/data-types.js	35.89% <0%> (-64.11%)	⬇️
lib/errors/database/timeout-error.js	40% <0%> (-60%)	⬇️
lib/query-interface.js	88.78% <0%> (-3.42%)	⬇️
lib/transaction.js	97.33% <0%> (-2.67%)	⬇️
lib/sequelize.js	94.68% <0%> (-1.25%)	⬇️
lib/dialects/abstract/query.js	91.02% <0%> (-0.97%)	⬇️
lib/dialects/abstract/query-generator.js	96.51% <0%> (-0.52%)	⬇️
lib/data-types.js	91% <0%> (-0.35%)	⬇️
... and 3 more

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[papb]

Hello! I see you are a first-time contributor, thank you for taking the time to help Sequelize! I hope to see more PRs from you in the future!

[papb]

Thank you!