rake db:migrate
した時に下記エラーが起きる場合。
rake aborted! Gem::LoadError: You have already activated rake 10.3.2, but your Gemfile requires rake 10.3.1.
<解決策>
bundle update rake
もう一度
rake db:migrate
してみると、通ります 
More than 5 years have passed since last update.
You have already activated rake 10.3.2, but your Gemfile requires rake 10.3.1.
Last updated at Posted at 2014-08-04
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