Upgrade Redis requirement check to 2.4.0 per https://github.com/mperham/sidekiq/pull/957

Closes #2222

Closes #2445

lib/tasks/gitlab/check.rake

@@ -278,7 +278,7 @@ namespace :gitlab do
         fix_and_rerun
       end
     end
-    
+
     def check_uploads
       print "Uploads directory setup correctly? ... "
@@ -331,15 +331,18 @@ namespace :gitlab do
     end
     def check_redis_version
-      print "Redis version >= 2.0.0? ... "
+      min_redis_version = "2.4.0"
+      print "Redis version >= #{min_redis_version}? ... "
       redis_version = run(%W(redis-cli --version))
-      if redis_version.try(:match, /redis-cli 2.\d.\d/) || redis_version.try(:match, /redis-cli 3.\d.\d/)
+      redis_version = redis_version.try(:match, /redis-cli (.*)/)
+      if redis_version &&
+          (Gem::Version.new(redis_version[1]) > Gem::Version.new(min_redis_version))
         puts "yes".green
       else
         puts "no".red
         try_fixing_it(
-          "Update your redis server to a version >= 2.0.0"
+          "Update your redis server to a version >= #{min_redis_version}"
         )
         for_more_information(
           "gitlab-public-wiki/wiki/Trouble-Shooting-Guide in section sidekiq"