Extend timeout

For some reason, `app.run spring_test_command` may take 100+ seconds.

```
`bundle check || bundle update --retry=2`	107.863471355
`bin/rake test /home/travis/build/mtsmfm/spring-debug/test/apps/tmp/test/controllers/posts_controller_test.rb`	105.624732034
`gem install activesupport --version '4.2.10'`	22.66985453
`bin/rails runner 'load Rails.root.join("script.rb")'`	11.518353908
`bin/rake test /home/travis/build/mtsmfm/spring-debug/test/apps/tmp/test/controllers/posts_controller_test.rb`	6.040077579
`bundle exec rails g scaffold post title:string`	4.525084902
```

https://travis-ci.org/mtsmfm/spring-debug/jobs/404996066

I got above result by applying the following patch:

```diff
diff --git a/lib/spring/test/application.rb b/lib/spring/test/application.rb
index 9a00618..93f129e 100644
--- a/lib/spring/test/application.rb
+++ b/lib/spring/test/application.rb
@@ -119,6 +119,8 @@ module Spring
         puts dump_streams(command, output) if ENV["SPRING_DEBUG"]

         @times << (Time.now - start_time) if @times
+        $times ||= []
+        $times << {command: command.to_s, time: Time.now - start_time}

         output.merge(status: status, command: command)
       rescue Timeout::Error
diff --git a/test/acceptance_test.rb b/test/acceptance_test.rb
index 665aff9..c24e82e 100644
--- a/test/acceptance_test.rb
+++ b/test/acceptance_test.rb
@@ -2,3 +2,11 @@ require_relative "helper"

 class AcceptanceTest < Spring::Test::AcceptanceTest
 end
+
+Minitest.after_run do
+  puts ?- * 100
+
+  $times.sort_by {|time| - time[:time] }.each do |time|
+    puts "`#{time[:command]}`\t#{time[:time]}"
+  end
+end
```

Author: mtsmfm

lib/spring/test/application.rb

@@ -3,7 +3,7 @@
 module Spring
   module Test
     class Application
-      DEFAULT_TIMEOUT = ENV['CI'] ? 30 : 10
+      DEFAULT_TIMEOUT = ENV['CI'] ? 300 : 10
 
       attr_reader :root, :spring_env