Update HAProxy documentation (2.4.0)

Author: simon04

assets/javascripts/templates/pages/about_tmpl.coffee

@@ -368,7 +368,7 @@ credits = [
     'https://raw.githubusercontent.com/wycats/handlebars.js/master/LICENSE'
   ], [
     'HAProxy',
-    '2020 Willy Tarreau, HAProxy contributors',
+    '2021 Willy Tarreau, HAProxy contributors',
     'GPLv2',
     'https://raw.githubusercontent.com/haproxy/haproxy/master/LICENSE'
   ], [

lib/docs/scrapers/haproxy.rb

@@ -16,10 +16,15 @@ class Haproxy < UrlScraper
     options[:follow_links] = false
 
     options[:attribution] = <<-HTML
-      &copy; 2020 Willy Tarreau, HAProxy contributors<br>
+      &copy; 2021 Willy Tarreau, HAProxy contributors<br>
       Licensed under the GNU General Public License version 2.
     HTML
 
+    version '2.4' do
+      self.release = '2.4.0'
+      self.base_url = "https://cbonte.github.io/haproxy-dconv/#{self.version}/"
+    end
+
     version '2.3' do
       self.release = '2.3.0'
       self.base_url = "http://cbonte.github.io/haproxy-dconv/#{self.version}/"