Revert "Revert "Merge pull request #39 from yohoushi/rails4.1.0""

This reverts commit f1036494d49e370b760ea963866a371c6cb9ebdf.
bundle update slim-rails
Fix rails version spec ~> 4.1.0
bundle update coffee-rails rails
activerecord-4.1.0 requires mysql2 (~> 0.3.13)
`bundle update rspec-rails  guard-rspec` to fix minitest bug
bundle update bullet

Update it to fix this https://github.com/seattlerb/minitest/issues/286
Make bootstrap_flash helper work with rails 4.1.0
bundle update acts-as-taggable-on
Add migrations for upgrading acts-as-taggable-on
Run rake db:migrate in bin/yohoushi command
Fix bug in starting serverengine in development

serverengine exited with the error uninitialized constant
Bullet::ActiveRecord.

The new version of bullet has to be loaded after rails is loaded.
Here the detail
https://github.com/flyerhzm/bullet/commit/dd105d9296c95383a3c892987a19bc4efa78d2ba
Define bootstrap_flash_helper inside
bundle update acts-as-taggable-on
Merge pull request #40 from yohoushi/rails4.1.0-again

Rails 4.1.0 again