Circle CIのbundle installが通らない(Rails5 & simple_form)

Question

Rails5アプリ内でSimple_formを使用しております。
simple_formはRails5用のブランチが用意されており、Gemfileには以下のように記述しています。
gem 'simple_form', github: 'kesha-antonov/simple_form', branch: 'rails-5-0'

開発環境ではこれで通るのですが、Circle CIに通した際にはエラーとなり手が出せない状態です。
sshで入って、libv8、simple_formをそれぞれインストール、'/home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746'を削除した後、正常に動作します。しかし、exit後、再度circle ci上でrunningすると同様のエラーが出てしまいます。
この場合どうすれば良いのでしょうか。。

bundle check --path=vendor/bundle || bundle install --path=vendor/bundle --jobs=4 --retry=3 
Your Gemfile lists the gem pry-rails (>= 0) more than once.
You should probably keep only one of them.
While it's not a problem now, it could cause errors if you change the version of just one of them later.
The following gems are missing
 * libv8 (3.16.14.15)
 * simple_form (3.2.1)
Install missing gems with `bundle install`
Your Gemfile lists the gem pry-rails (>= 0) more than once.
You should probably keep only one of them.
While it's not a problem now, it could cause errors if you change the version of just one of them later.
Fetching gem metadata from https://rubygems.org/
Fetching version metadata from https://rubygems.org/
Fetching dependency metadata from https://rubygems.org/
Fetching git://github.com/kesha-antonov/simple_form.git
fatal: Refusing to fetch into current branch refs/heads/master of non-bare repository
Retrying git fetch --force --quiet --tags 'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*" due to error (2/4): Bundler::Source::Git::GitCommandError Git error: command `git fetch --force --quiet --tags 'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*"` in directory /home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746 has failed.
If this error persists you could try removing the cache directory '/home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746'
fatal: Refusing to fetch into current branch refs/heads/master of non-bare repository
Retrying git fetch --force --quiet --tags 'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*" due to error (3/4): Bundler::Source::Git::GitCommandError Git error: command `git fetch --force --quiet --tags 'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*"` in directory /home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746 has failed.
If this error persists you could try removing the cache directory '/home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746'
fatal: Refusing to fetch into current branch refs/heads/master of non-bare repository
Retrying git fetch --force --quiet --tags 'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*" due to error (4/4): Bundler::Source::Git::GitCommandError Git error: command `git fetch --force --quiet --tags 'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*"` in directory /home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746 has failed.
If this error persists you could try removing the cache directory '/home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746'
fatal: Refusing to fetch into current branch refs/heads/master of non-bare repository
it error: command `git fetch --force --quiet --tags
'git://github.com/kesha-antonov/simple_form.git' "refs/heads/*:refs/heads/*"` in
directory
/home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746
has failed.
If this error persists you could try removing the cache directory
'/home/ubuntu/app/vendor/bundle/ruby/2.3.0/cache/bundler/git/simple_form-f9aa705c79765ebcba3e937a1357edd7854a4746'

bundle check --path=vendor/bundle || bundle install --path=vendor/bundle --jobs=4 --retry=3  returned exit code 11

Action failed: bundle install