Heroku运行rake db：迁移错误，“没有这样的文件加载 - bundler / setup”

Question

我正在尝试“heroku run rake db：migrate”，并收到此错误：

es-MacBook-Pro:project e$ heroku run rake db:migrate
Running rake db:migrate attached to terminal... up, run.1
(in /app)
rake aborted!
no such file to load -- bundler/setup
<internal:lib/rubygems/custom_require>:29:in `require'
<internal:lib/rubygems/custom_require>:29:in `require'
/app/config/boot.rb:6:in `<top (required)>'
<internal:lib/rubygems/custom_require>:29:in `require'
<internal:lib/rubygems/custom_require>:29:in `require'
/app/config/application.rb:1:in `<top (required)>'
<internal:lib/rubygems/custom_require>:29:in `require'
<internal:lib/rubygems/custom_require>:29:in `require'
/app/Rakefile:5:in `<top (required)>'
/usr/local/lib/ruby/1.9.1/rake.rb:2373:in `load'
/usr/local/lib/ruby/1.9.1/rake.rb:2373:in `raw_load_rakefile'
/usr/local/lib/ruby/1.9.1/rake.rb:2007:in `block in load_rakefile'
/usr/local/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
/usr/local/lib/ruby/1.9.1/rake.rb:2006:in `load_rakefile'
/usr/local/lib/ruby/1.9.1/rake.rb:1991:in `run'
/usr/local/bin/rake:31:in `<main>'

我不知道如何解释这个错误。有没有人有任何线索？