Use carrierwave-magic 0.0.4 for MIME type check

ref.
  http://qiita.com/k-okishima@github/items/ea9f5862d4fbf4a9fef8
  https://github.com/glebtv/carrierwave-magic
Run "bin/bundle"

"libmagic-dev" package is needed on Ubuntu.
Implement MIME type validation

ref. http://qiita.com/k-okishima@github/items/ea9f5862d4fbf4a9fef8
Merge branch 'mime-type-check'