Fix search function in docs

[rly]

Motivation

See NeurodataWithoutBorders/pynwb#1671

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c9573c5) 87.79% compared to head (51795ec) 87.79%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #840   +/-   ##
=======================================
  Coverage   87.79%   87.79%           
=======================================
  Files          44       44           
  Lines        8950     8950           
  Branches     2062     2062           
=======================================
  Hits         7858     7858           
  Misses        779      779           
  Partials      313      313           

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