Download chromedriver during container build

If it's too outdated it leads to weird failures in the test suite
because we disallow outside requests in it.

Dockerfile

@@ -20,7 +20,8 @@ WORKDIR /osem/
 RUN bundle config set --local path 'vendor/bundle'; \
     bundle install --jobs=4 --retry=3
 
-# Install our process manager
-RUN gem install foreman
+# Install our process manager / update chromedriver
+RUN gem install foreman; \
+    bundle exec bin/rails webdrivers:chromedriver:update
 
 CMD ["foreman", "start"]

Gemfile

@@ -213,9 +213,7 @@ group :test do
   # as test framework
   gem 'capybara'
   gem 'database_cleaner'
-  gem 'geckodriver-helper'
   gem 'rspec-rails'
-  gem 'webdrivers'
   # for measuring test coverage
   gem 'simplecov-cobertura'
   # for describing models
@@ -239,6 +237,9 @@ group :test do
 end
 
 group :development, :test do
+  # as capybara driver
+  gem 'webdrivers'
+  gem 'geckodriver-helper'
   # as debugger
   gem 'byebug'
   # to test new rails version