Remove stale comment

We're now passed the issue described in the FIXME.

Gemfile

@@ -2,23 +2,6 @@ source 'https://rubygems.org'
 
 gem 'warbler', git: 'https://github.com/jruby/warbler' if RUBY_PLATFORM == 'java'
 
-# FIXME:
-#
-# There's an issue in 1.12.5 that causes XHTML elements to be generated badly,
-# causing Gollum's test suite to fail.[1] The issue has been fixed upstream,
-# but we're still waiting for a new Nokogiri point release.
-#
-# However, 1.12.5 is a security patch, so we don't want end users to use an
-# older version of Nokogiri. But this is safe to do in our CI environment.
-#
-# Once there's a new Nokogiri release, we can remove this dependency and JRuby
-# CI should pass normally again.
-#
-# Note that Nokogiri 1.11+ does not support Ruby v2.4.x anymore. So to make our
-# current CI workflows pass, we should only try to install this version of
-# Nokogiri for newer Ruby versions.
-
-
 group :test do
   gem 'selenium-webdriver', require: false
   gem 'capybara', require: false