diff --git a/.rubocop.yml b/.rubocop.yml
index 1407be2..20f05fa 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,6 +1,7 @@
 AllCops:
-  TargetRubyVersion: 2.5
   DisplayCopNames: true
+  NewCops: enable
+  TargetRubyVersion: 2.5
 
 Bundler/DuplicatedGem:
   Enabled: false
diff --git a/lib/simplecov-html.rb b/lib/simplecov-html.rb
index 7e725f5..2887811 100644
--- a/lib/simplecov-html.rb
+++ b/lib/simplecov-html.rb
@@ -10,8 +10,8 @@
 # Ensure we are using a compatible version of SimpleCov
 major, minor, patch = SimpleCov::VERSION.scan(/\d+/).first(3).map(&:to_i)
 if major < 0 || minor < 9 || patch < 0
-  raise "The version of SimpleCov you are using is too old. "\
-  "Please update with `gem install simplecov` or `bundle update simplecov`"
+  raise "The version of SimpleCov you are using is too old. " \
+        "Please update with `gem install simplecov` or `bundle update simplecov`"
 end
 
 module SimpleCov
@@ -94,7 +94,7 @@ def asset_inline(name)
           ".css" => "text/css",
         }[File.extname(name)]
 
-        base64_content = Base64.strict_encode64 File.open(path).read
+        base64_content = Base64.strict_encode64 File.read(path)
         "data:#{content_type};base64,#{base64_content}"
       end
 
diff --git a/simplecov-html.gemspec b/simplecov-html.gemspec
index f2d780e..48103af 100644
--- a/simplecov-html.gemspec
+++ b/simplecov-html.gemspec
@@ -22,7 +22,7 @@ Gem::Specification.new do |gem|
         f.start_with?(*%w[bin/ test/ spec/ features/ .git .github appveyor Gemfile assets .rubocop.yml Guardfile])
     end
   end
-  gem.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
   gem.executables   = `git ls-files -- bin/*`.split("\n").map { |f| File.basename(f) }
   gem.require_paths = ["lib"]
+  gem.metadata["rubygems_mfa_required"] = "true"
 end