So we were deploying to heroku and we have a gem as part of project thats forked from original and heroku didnt like it at all and we got an error like so

Removing .DS_Store files
remote: -----> Ruby app detected
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.0.0
remote: -----> Installing dependencies using 1.9.7
remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
remote:        Fetching gem metadata from
remote:        Fetching version metadata from
remote:        Fetching dependency metadata from
remote:        Fetching
remote:        Host key verification failed.
remote:        fatal: Could not read from remote repository.
remote:        Please make sure you have the correct access rights
remote:        and the repository exists.
remote:        Retrying git clone '' "/tmp/build_aab7506f5342f75413d3d85d01e2a558/vendor/bundle/ruby/2.0.0/cache/bundler/git/acts_as_follower-5ebd9d15f4ab98d51b4735c6146a547d602764cb" --bare --no-hardlinks --quiet due to error (2/3): Bundler::Source::Git::GitCommandError Git error: command `git clone '' "/tmp/build_aab7506f5342f75413d3d85d01e2a558/vendor/bundle/ruby/2.0.0/cache/bundler/git/acts_as_follower-5ebd9d15f4ab98d51b4735c6146a547d602764cb" --bare --no-hardlinks --quiet` in directory /tmp/build_aab7506f5342f75413d3d85d01e2a558 has failed.

In our gem file we had

gem 'acts_as_follower', git: ""

Now this left us scratching our heads as haven't seen this issue before. After some reading we found the issue

The… URL is the writable SSH version, which requires authentication with an SSH key connected to a GitHub account that has write access to the repository.
The git://… URL is the public, read-only version.
Since the gem you're using is in a public GitHub repository, you can also use this shorthand in your Gemfile:

So we changed our gem to to below and all good again in the world of development

gem 'acts_as_follower', github: "siassaj/acts_as_follower"