bundle install clone git repo 後無法切換到正確的 gemspec 版本 gem "techbang-authentication", "0.4.0", :github => "techbang-authentication" 2. 指定 git tag 或 git ref gem "techbang-authentication", :tag => "0.4.0", :github => "techbang-authentication" gem "techbang-authentication", :ref => "4aded", :github => "techbang-authentication" 3. 使用 private gem server 管理 gem 版本 source "https://private.gem.server" gem "techbang-authentication", "~> 0.4.0"