Bump ex_doc from 0.28.3 to 0.28.4

Bumps ex_doc from 0.28.3 to 0.28.4.

Changelog

Sourced from ex_doc's changelog.

v0.28.4 (2022-04-28)

• Enhancements

  • Add a toast when changing theme via keyboard
  • Automatically convert .livemd links to .html ones
  • Show programming language in HTML footer

• Bug fixes

  • Properly escape %/2 special form
  • Improve ranking of exact-matching modules in search

Commits

• d152fe9 Release v0.28.4
• 46df46e Automatically convert .livemd links
• 363edfa Remove race in tests
• 0fa8c24 Simplify title extraction, closes #1563
• 2b2bcbe Escape &%/2 special form (#1562)
• f8aad1f Use tmp_dir in template tests (#1561)
• cf8530a Optimize html/epub tests by making them asyncronous by using tmp_dir tag (#1557)
• 8b42650 Show programming language in HTML footer (#1560)
• d01098a Mention how to extend syntax highlighting in the README
• a320eab Add tests for license files and all files in .build (#1556)
• Additional commits viewable in compare view