我正在尝试为Heroku设置数据库。我已经尝试过gem install bundler / bundle install，安装得很好。但是我仍然遇到这个错误。有什么建议？谢谢！
heroku run rake db:migrate
Running rake db:migrate on ⬢ mycapstoneeventbrighter... up, run.2960
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- bundler (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from /app/bin/spring:8:in `<top (required)>'
from /app/bin/rake:3:in `load'
from /app/bin/rake:3:in `<main>'