add travis.yml

Many test fails in the current master branch as followings. Let's use travis. 

    1) ServerEngine::Daemon run and graceful stop
     Failure/Error: test_state(:server_stop_graceful).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/daemon_spec.rb:18:in `block (2 levels) in <top (required)>'
    
    2) ServerEngine::Daemon signals
     Failure/Error: test_state(:server_reload).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/daemon_spec.rb:32:in `block (2 levels) in <top (required)>'
    
    3) ServerEngine::MultiWorkerServer scale up
     Failure/Error: test_state(:worker_run).should == 3
       expected: 3
            got: 5 (using ==)
     # ./spec/multi_process_server_spec.rb:22:in `block (3 levels) in <top (required)>'
    
    4) ServerEngine::MultiWorkerServer scale down
     Failure/Error: test_state(:worker_stop).should == 2
       expected: 2
            got: 0 (using ==)
     # ./spec/multi_process_server_spec.rb:50:in `block (3 levels) in <top (required)>'
    
    5) ServerEngine::SignalThread call handler
     Failure/Error: n.should == 1
     ThreadError:
       can't be called from trap context
     # ./lib/serverengine/signal_thread.rb:138:in `unlock'
     # ./lib/serverengine/signal_thread.rb:138:in `ensure in enqueue'
     # ./lib/serverengine/signal_thread.rb:138:in `enqueue'
     # ./lib/serverengine/signal_thread.rb:46:in `block in trap'
     # ./spec/signal_thread_spec.rb:21:in `block (2 levels) in <top (required)>'
    
    6) ServerEngine::SignalThread signal in handler
     Failure/Error: sleep 1
     ThreadError:
       can't be called from trap context
     # ./lib/serverengine/signal_thread.rb:138:in `unlock'
     # ./lib/serverengine/signal_thread.rb:138:in `ensure in enqueue'
     # ./lib/serverengine/signal_thread.rb:138:in `enqueue'
     # ./lib/serverengine/signal_thread.rb:46:in `block in trap'
     # ./spec/signal_thread_spec.rb:48:in `call'
     # ./spec/signal_thread_spec.rb:48:in `sleep'
     # ./spec/signal_thread_spec.rb:48:in `block (2 levels) in <top (required)>'
    
    7) ServerEngine::SignalThread stop in handler
     Failure/Error: t.join
     ThreadError:
       can't be called from trap context
     # ./lib/serverengine/signal_thread.rb:138:in `unlock'
     # ./lib/serverengine/signal_thread.rb:138:in `ensure in enqueue'
     # ./lib/serverengine/signal_thread.rb:138:in `enqueue'
     # ./lib/serverengine/signal_thread.rb:46:in `block in trap'
     # ./spec/signal_thread_spec.rb:62:in `call'
     # ./spec/signal_thread_spec.rb:62:in `join'
     # ./spec/signal_thread_spec.rb:62:in `block (2 levels) in <top (required)>'
    
    8) ServerEngine::SignalThread should not deadlock
     Failure/Error: Thread.new do
     ThreadError:
       can't be called from trap context
     # ./lib/serverengine/signal_thread.rb:138:in `unlock'
     # ./lib/serverengine/signal_thread.rb:138:in `ensure in enqueue'
     # ./lib/serverengine/signal_thread.rb:138:in `enqueue'
     # ./lib/serverengine/signal_thread.rb:46:in `block in trap'
     # ./spec/signal_thread_spec.rb:73:in `call'
     # ./spec/signal_thread_spec.rb:73:in `new'
     # ./spec/signal_thread_spec.rb:73:in `block (3 levels) in <top (required)>'
     # ./spec/signal_thread_spec.rb:72:in `each'
     # ./spec/signal_thread_spec.rb:72:in `map'
    
    9) ServerEngine::Supervisor start and graceful stop
     Failure/Error: test_state(:server_before_run).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/supervisor_spec.rb:19:in `block (2 levels) in <top (required)>'
    
    10) ServerEngine::Supervisor immediate stop
     Failure/Error: test_state(:server_stop).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/supervisor_spec.rb:44:in `block (2 levels) in <top (required)>'
    
    11) ServerEngine::Supervisor graceful restart
     Failure/Error: test_state(:server_stop).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/supervisor_spec.rb:63:in `block (2 levels) in <top (required)>'
    
    12) ServerEngine::Supervisor immediate restart
     Failure/Error: test_state(:server_stop).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/supervisor_spec.rb:84:in `block (2 levels) in <top (required)>'
    
    13) ServerEngine::Supervisor reload
     Failure/Error: test_state(:server_stop).should == 1
       expected: 1
            got: 0 (using ==)
     # ./spec/supervisor_spec.rb:105:in `block (2 levels) in <top (required)>'