Installation is pretty standard:

gem install rspec-tap-formatters

You can install using bundler also but do not require it in Gemfile. Make sure to use it as a test dependency:

group :test do
  # other gems
  gem 'rspec-tap-formatter', '~> 0.1.0', require: false
end

You can also install using the GitHub package registry:

source 'https://rubygems.pkg.github.com/avmnu-sng' do
  gem 'rspec-tap-formatter', '~> 0.1.0', require: false
end