Fix failing specs due when stopping `MessageBus::TimerThread`.

Fix failing specs due when stopping MessageBus::TimerThread.

The thread may be dead before Thread#wakeup is called.

diff --git a/lib/message_bus/timer_thread.rb b/lib/message_bus/timer_thread.rb
index ae1d25c..88b6e41 100644
--- a/lib/message_bus/timer_thread.rb
+++ b/lib/message_bus/timer_thread.rb
@@ -45,7 +45,14 @@ class MessageBus::TimerThread
     while running
       @mutex.synchronize do
         running = @thread && @thread.alive?
-        @thread.wakeup if running
+
+        if running
+          begin
+            @thread.wakeup
+          rescue ThreadError
+            raise if @thread.alive?
+          end
+        end
       end
       sleep 0
     end

GitHub sha: 60f8288f