fix bug in workers.rb flush

lib/amplitude/workers.rb

@@ -40,8 +40,8 @@ def stop
     end
 
     def flush
+      events = @storage.pull_all
       Concurrent::Future.execute do
-        events = @storage.pull_all
         if events && !events.empty?
           send(events)
         end

spec/amplitude/client_spec.rb

@@ -30,7 +30,6 @@ def setup_stub
         25.times do |i|
           @client.track(BaseEvent.new('test_event', user_id: 'test_user_id', event_properties: { 'id' => i }))
         end
-        sleep(1)
         futures = @client.flush
         futures.each do |flush_future|
           flush_future&.value

spec/spec_helper.rb

@@ -7,5 +7,4 @@
   add_filter '/spec/'
   add_filter '/vendor/'
 end
-
 WebMock.disable_net_connect!(allow_localhost: true)