Appease RuboCop

Fix the following errors pointed out by RuboCop:

Rakefile:27:5: C: [Corrected] Style/TrailingCommaInArguments: Put a comma after the last parameter of a multiline method call.
    with_toc_data: true
    ^^^^^^^^^^^^^^^^^^^
lib/html_proofer.rb:7:3: C: [Corrected] Style/TrailingCommaInArguments: Put a comma after the last parameter of a multiline method call.
  "html_proofer" => "HTMLProofer"
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Rakefile

@@ -24,7 +24,7 @@ task :proof_readme do
   require "redcarpet"
 
   renderer = Redcarpet::Render::HTML.new(\
-    with_toc_data: true
+    with_toc_data: true,
   )
   redcarpet = Redcarpet::Markdown.new(renderer)
   html = redcarpet.render(File.read("README.md"))

lib/html_proofer.rb

@@ -4,7 +4,7 @@
 lib_dir = File.join(File.dirname(__dir__), "lib")
 gem_loader = Zeitwerk::Loader.for_gem
 gem_loader.inflector.inflect(
-  "html_proofer" => "HTMLProofer"
+  "html_proofer" => "HTMLProofer",
 )
 gem_loader.ignore(File.join(lib_dir, "html-proofer.rb"))
 gem_loader.setup