当我尝试通过 rake db：migrate 应用迁移时，出现以下错误：
rake aborted!
Gem::LoadError: You have already activated rake 12.0.0, but your
Gemfile requires rake 10.4.2. Prepending `bundle exec` to your command
may solve this.
/home/jeyjeyanischixx/CaprisePro/config/boot.rb:3:in `<top (required)>'
/home/jeyjeyanischixx/CaprisePro/config/application.rb:1:in `<top (required)>'
/home/jeyjeyanischixx/CaprisePro/Rakefile:4:in `<top (required)>'
/home/jeyjeyanischixx/.rvm/gems/ruby-2.4.1@global/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
然后当我在此命令之前添加bundle exec时，我得到了这个：
Could not find nokogiri-1.8.2 in any of the sources
Run `bundle install` to install missing gems.
但我已经成功安装了所有宝石（包括nokogiri和rake两个版本（10.4.2和12.0.0））。
Rails：4.2.10; Ruby：2.4.1