Update Rails version to 4.1.4

To avoid CVE-2014-3482 and CVE-2014-3483.

ref.
  https://groups.google.com/forum/#!msg/rubyonrails-security/wDxePLJGZdI/WP7EasCJTA4J
  http://weblog.rubyonrails.org/2014/7/2/Rails_3_2_19_4_0_7_and_4_1_3_have_been_released/
  http://weblog.rubyonrails.org/2014/7/2/Rails_4_0_8_and_4_1_4_have_been_released/
Run "bundle update"
Run "rake rails:update"

Keep "config/routes.rb" and "config/secrets.yml"

"config/environments/production.rb" lost its changesets by overwriting.
It will be reverted in next commit.

ref. http://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html
Modify serve_static_assets to true

To enable asset pipeline precompilation on Heroku

ref. https://devcenter.heroku.com/articles/rails-4-asset-pipeline
Merge branch 'rails-update'