Undercover gem requires rugged? But fails

Rails
1

I’m trying to install undercover.

I can’t run rspec anymore as I get:

( how )% bundle exec rspec
Could not find rugged-0.27.5 in any of the sources
Run `bundle install` to install missing gems.

I put undercover in my Gemfile (then added rugged since it complained):

Gemfile excerpt 
# More gems...

group :development, :test do
  gem 'byebug', platform: :mri
  gem 'fabrication'
  gem 'guard'
  gem 'pry'
  gem 'pry-byebug'
  gem 'rb-inotify', '~> 0.9'
  gem 'rspec'
  gem 'rspec-rails', '~> 3.7'
  gem 'rugged' # Apparently this is broken
  gem 'shoulda', require: false
  gem 'shoulda-matchers'
end

# More gems...

group :test do
  gem 'database_cleaner'
  gem 'rails-controller-testing'
  gem 'simplecov', require: false
  gem 'simplecov-lcov', require: false
  gem 'undercover'
end

I installed rugged successfully using:

sudo emerge libgit2 # version is 0.27.5
bundle config build.rugged --use-system-libraries
bundle install # successful, see below
results from bundle install 
...
Using rails 5.2.1
Using rails-controller-testing 1.0.2
Using ruby-graphviz 1.2.3
Using rails-erd 1.5.2
Using rspec-rails 3.8.1
Using tty-which 0.3.0
Using rubycritic 3.5.2
Using rugged 0.27.5
Using seed_dump 3.3.1
Using shoulda-context 1.2.2
Using shoulda-matchers 3.1.2
Using shoulda 3.6.0
Using simplecov-html 0.10.2
Using simplecov 0.16.1
Using simplecov-lcov 0.7.0
Using spring 2.0.2
Using undercover 0.1.4
Using uuid_parameter 0.2.4
Bundle complete! 49 Gemfile dependencies, 152 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.

Using gem install rugged -- --use-system-libraries works as well.

But then:

( how )% bundle exec rspec
Could not find rugged-0.27.5 in any of the sources
Run `bundle install` to install missing gems.

Huh? I’m not willing to bundle libgit2 with rugged as mentioned in the README since I already have the libraries. Did you ever have this issue?

I’m running Rails 5.2.1 and Ruby 2.5.3.