CompatHelper: bump compat for "Documenter" to "0.27" for package docs

[github-actions]

This pull request changes the compat entry for the Documenter package from 0.26 to 0.26, 0.27 for package docs.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

Merging #77 (1ba41d0) into master (a98f057) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #77   +/-   ##
=======================================
  Coverage   97.57%   97.57%           
=======================================
  Files           7        7           
  Lines         206      206           
=======================================
  Hits          201      201           
  Misses          5        5           

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