parallel.rb: Thread.exclusive is deprecated, use Thread::Mutex

[dinsdalepiranha]

Went from trusty (ruby 1.9.1) to bionic (ruby 2.5.0) but it seems the version of parallel that rubycon requires is using something deprecated:

$ rubycon list
Thread.exclusive is deprecated, use Thread::Mutex
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:224:in `block (2 levels) in work_in_threads'
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:221:in `loop'
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:221:in `block in work_in_threads'
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:65:in `block (2 levels) in in_threads'
Thread.exclusive is deprecated, use Thread::Mutex
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:224:in `block (2 levels) in work_in_threads'
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:221:in `loop'
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:221:in `block in work_in_threads'
/var/lib/gems/2.5.0/gems/parallel-0.9.2/lib/parallel.rb:65:in `block (2 levels) in in_threads'
Server                  Map     Players      Ping
fragpalace         de_dust2        0/18        29