Heroku，捆绑程序因缺少依赖项而失败

我最近在尝试在Heroku上部署我的Rails应用程序时遇到了麻烦。过去，我毫无问题地在Heroku上部署了应用程序，但是Heroku不再支持ruby 2.0.0。他们建议增加ruby "2.2.4"的Gemfile，这是我做的。我的开头Gemfile如下：

source 'https://rubygems.org'
ruby "2.2.4"

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.2.0'
# Use pg as the database for Active Record
gem 'pg'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.1.0'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
...

因此，我bundle install在计算机上运行的版本为1.7.8，没有问题。我什至可以在生产模式下运行我的应用程序。但是，当我尝试在Heroku上部署应用程序时，我得到了以下信息：

-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.2.4
-----> Installing dependencies using bundler 1.11.2
       Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
       Fetching gem metadata from https://rubygems.org/...........
       Fetching version metadata from https://rubygems.org/...
       Fetching dependency metadata from https://rubygems.org/..
       Using rake 10.4.2
       Installing i18n 0.7.0
       Installing minitest 5.4.3
       Installing json 1.8.3 with native extensions
       Installing thread_safe 0.3.4
       Installing builder 3.2.2
       Installing erubis 2.7.0
       Your Gemfile.lock is corrupt. The following gem is missing from the DEPENDENCIES
       section: 'mini_portile2'
       Bundler Output: Fetching gem metadata from https://rubygems.org/...........
       Fetching version metadata from https://rubygems.org/...
       Fetching dependency metadata from https://rubygems.org/..
       Using rake 10.4.2
       Installing i18n 0.7.0
       Installing minitest 5.4.3
       Installing json 1.8.3 with native extensions
       Installing thread_safe 0.3.4
       Installing builder 3.2.2
       Installing erubis 2.7.0
       Your Gemfile.lock is corrupt. The following gem is missing from the DEPENDENCIES
       section: 'mini_portile2'
 !
 !     Failed to install gems via Bundler.
 !
 !     Push rejected, failed to compile Ruby app

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