Nunca inclua tokens de acesso GitHub em seu Gemfile novamente

https://gist.github.com/haihappen/bd5cfc2429dc14287bc5

# Be sure to have GITHUB_TOKEN set to your access token... via `export` or via .rbenv-vars for example. 
source 'https://rubygems.org'
git_source(:private_github) { |repo_name| "https://#{ENV.fetch('GITHUB_TOKEN')}:x-oauth-basic@github.com/#{repo_name}.git" }

gem 'my-super-secret-gem', private_github: 'haihappen/my-super-secret-gem'