masterからのcherry-pick(37f6eb0c695b3da722c1e5922b04904bdce24320)
  rake db:migrate に環境名を渡すよう追記。ついでにいらない文章を削除。

  Conflicts:
    README.md
Modified badges (and remove coveralls badge)
tweak article model
add article-edit spec
increase Capybara.default_wait_time for travis.ci testing
poltergeist enabled
use phantomjs and fix test