[rubygems/rubygems] gemfile.5: Quote default glob to escape Markdown

For consistency, I chose code format over plaintext escaping.

lib/bundler/man/gemfile.5.ronn

@@ -518,7 +518,7 @@ paths.
 
 The `gemspec` method supports optional `:path`, `:glob`, `:name`, and `:development_group`
 options, which control where bundler looks for the `.gemspec`, the glob it uses to look
-for the gemspec (defaults to: "{,*,*/*}.gemspec"), what named `.gemspec` it uses
+for the gemspec (defaults to: `{,*,*/*}.gemspec`), what named `.gemspec` it uses
 (if more than one is present), and which group development dependencies are included in.
 
 When a `gemspec` dependency encounters version conflicts during resolution, the