Heroku 推送失败是由 Gemfile 中的以下 gem 引起的：
gem 'mongoid_taggable_with_context', :git => 'git@github.com:lgs/mongoid_taggable_with_context.git'
lsoave@ubuntu:~/rails/github/gitwatcher$ git push heroku +master
Counting objects: 233, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (196/196), done.
Writing objects: 100% (199/199), 286.76 KiB | 62 KiB/s, done.
Total 199 (delta 160), reused 2 (delta 2)
-----> Heroku receiving push
-----> Ruby/Rails app detected
-----> Using Ruby version: ruby-1.9.3
-----> Installing dependencies using Bundler version 1.2.0.rc
Running: bundle install --without development:test --path vendor/bundle --binstubs bin/ --deployment
Fetching gem metadata from http://rubygems.org/.......
Fetching gem metadata from http://rubygems.org/..
Updating git://github.com/rweng/jquery-datatables-rails.git
Fetching git@github.com:lgs/mongoid_taggable_with_context.git
Host key verification failed.
fatal: The remote end hung up unexpectedly
Git error: command `git clone 'git@github.com:lgs/mongoid_taggable_with_context.git' "/tmp/build_1mck6mlqu6pko/vendor/bundle/ruby/1.9.1/cache/bundler/git/mongoid_taggable_with_context-cf14763a075f5ec09e40c360c8537afb67040db7" --bare --no-hardlinks` in directory /tmp/build_1mck6mlqu6pko has failed.
!
! Failed to install gems via Bundler.
!
! Heroku push rejected, failed to compile Ruby/rails app
To git@heroku.com:gitwatcher.git
! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:gitwatcher.git'
lsoave@ubuntu:~/rails/github/gitwatcher$