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

[github-actions[bot]]

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.

[coveralls]

Pull Request Test Coverage Report for Build 926958321

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.525%

---

Totals
Change from base Build 888541031:	0.0%
Covered Lines:	1734
Relevant Lines:	1778

---

💛 - Coveralls