Use Rubygems 3.0.3 on CI to fix bug with Ruby 2.5 stdlib

Author: rafaelfranca

.travis.yml

@@ -42,7 +42,7 @@ matrix:
     - rvm: ruby-head
   fast_finish: true
 before_install:
-  - gem update --system 2.6.14
+  - gem update --system 3.0.3
 before_script:
   - "[ $TRAVIS_RUBY_VERSION = \"1.9.3\" ] && travis_retry gem install mime-types --version \"~> 2\" || true"
   - "[ $TRAVIS_RUBY_VERSION = \"1.9.3\" -o $TRAVIS_RUBY_VERSION = \"2.0.0\" ] && travis_retry gem install nokogiri --version \"~> 1.6.8\" || true"

lib/spring/test/application_generator.rb

@@ -134,7 +134,7 @@ def build_and_install_gems
             system("gem build #{name}.gemspec 2>&1")
           end
 
-          application.run! "gem install #{spec.gem_dir}/#{name}-*.gem --no-ri --no-rdoc", timeout: nil
+          application.run! "gem install #{spec.gem_dir}/#{name}-*.gem --no-doc", timeout: nil
         end
       end