Fix wrong condition when replacing a fork

As reported in #305. I haven't managed to reproduce this, but the right
logic is definitely the one in this commit. Thanks to @Darhazer for
catching this.

Author: rosa

lib/solid_queue/supervisor/fork_supervisor.rb

@@ -84,7 +84,7 @@ def reap_terminated_forks
           pid, status = ::Process.waitpid2(-1, ::Process::WNOHANG)
           break unless pid
 
-          if (terminated_fork = forks.delete(pid)) && !status.exited? || status.exitstatus > 0
+          if (terminated_fork = forks.delete(pid)) && (!status.exited? || status.exitstatus > 0)
             handle_claimed_jobs_by(terminated_fork, status)
           end