Remove Gemfile.lock from git repo

[liijunwei]

• gem should not check Gemfile.lock into git, app do
• ref: https://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/

ref gems

• https://github.com/mperham/sidekiq
• https://github.com/ged/ruby-pg
• https://github.com/rubocop/rubocop
• https://github.com/rest-client/rest-client
• ...