Update epubcheck-ruby requirement from ~> 4.2.4.0 to ~> 4.2.5.0 (#392)

Updates the requirements on [epubcheck-ruby](https://github.com/takahashim/epubcheck-ruby) to permit the latest version.
- [Release notes](https://github.com/takahashim/epubcheck-ruby/releases)
- [Commits](takahashim/epubcheck-ruby@v4.2.4.0...v4.2.5.0)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile

@@ -13,5 +13,5 @@ end
 
 group :optional do
   # epubcheck-ruby might be safe to be converted into runtime dependency, but could have issues when packaged into asciidoctorj-epub3
-  gem 'epubcheck-ruby', '~> 4.2.4.0'
+  gem 'epubcheck-ruby', '~> 4.2.5.0'
 end