Fix `Style/StringLiterals` violations for Active Storage

```
% be rubocop -a --only Style/StringLiterals activestorage
Inspecting 74 files
........................................CCCCCCCCCC.C........CC.......C.C..

(snip)

74 files inspected, 31 offenses detected, 31 offenses corrected
```

7 files changed, 11 insertions, 11 deletions

diff --git a/activestorage/test/dummy/config/application.rb b/activestorage/test/dummy/config/application.rb
index 7c8c2575ee..5c59401358 100644
--- a/activestorage/test/dummy/config/application.rb
+++ b/activestorage/test/dummy/config/application.rb
@@ -1,4 +1,4 @@
-require_relative 'boot'
+require_relative "boot"
 
 require "rails"
 require "active_model/railtie"
diff --git a/activestorage/test/dummy/config/boot.rb b/activestorage/test/dummy/config/boot.rb
index c9aef85d40..116591a4ed 100644
--- a/activestorage/test/dummy/config/boot.rb
+++ b/activestorage/test/dummy/config/boot.rb
@@ -1,5 +1,5 @@
 # Set up gems listed in the Gemfile.
-ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../../Gemfile', __dir__)
+ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../../../Gemfile", __dir__)
 
-require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
-$LOAD_PATH.unshift File.expand_path('../../../lib', __dir__)
+require "bundler/setup" if File.exist?(ENV["BUNDLE_GEMFILE"])
+$LOAD_PATH.unshift File.expand_path("../../../lib", __dir__)
diff --git a/activestorage/test/dummy/config/environment.rb b/activestorage/test/dummy/config/environment.rb
index 426333bb46..cac5315775 100644
--- a/activestorage/test/dummy/config/environment.rb
+++ b/activestorage/test/dummy/config/environment.rb
@@ -1,5 +1,5 @@
 # Load the Rails application.
-require_relative 'application'
+require_relative "application"
 
 # Initialize the Rails application.
 Rails.application.initialize!
diff --git a/activestorage/test/dummy/config/environments/development.rb b/activestorage/test/dummy/config/environments/development.rb
index 503375dede..5f3d463210 100644
--- a/activestorage/test/dummy/config/environments/development.rb
+++ b/activestorage/test/dummy/config/environments/development.rb
@@ -13,12 +13,12 @@ Rails.application.configure do
   config.consider_all_requests_local = true
 
   # Enable/disable caching. By default caching is disabled.
-  if Rails.root.join('tmp/caching-dev.txt').exist?
+  if Rails.root.join("tmp/caching-dev.txt").exist?
     config.action_controller.perform_caching = true
 
     config.cache_store = :memory_store
     config.public_file_server.headers = {
-      'Cache-Control' => "public, max-age=#{2.days.seconds.to_i}"
+      "Cache-Control" => "public, max-age=#{2.days.seconds.to_i}"
     }
   else
     config.action_controller.perform_caching = false
diff --git a/activestorage/test/dummy/config/environments/production.rb b/activestorage/test/dummy/config/environments/production.rb
index 35a30e084a..343da23f0b 100644
--- a/activestorage/test/dummy/config/environments/production.rb
+++ b/activestorage/test/dummy/config/environments/production.rb
@@ -21,7 +21,7 @@ Rails.application.configure do
 
   # Disable serving static files from the `/public` folder by default since
   # Apache or NGINX already handles this.
-  config.public_file_server.enabled = ENV['RAILS_SERVE_STATIC_FILES'].present?
+  config.public_file_server.enabled = ENV["RAILS_SERVE_STATIC_FILES"].present?
 
   # Compress JavaScripts and CSS.
   config.assets.js_compressor = :uglifier
diff --git a/activestorage/test/dummy/config/environments/test.rb b/activestorage/test/dummy/config/environments/test.rb
index 4380dfc0cd..4f2c048600 100644
--- a/activestorage/test/dummy/config/environments/test.rb
+++ b/activestorage/test/dummy/config/environments/test.rb
@@ -15,7 +15,7 @@ Rails.application.configure do
   # Configure public file server for tests with Cache-Control for performance.
   config.public_file_server.enabled = true
   config.public_file_server.headers = {
-    'Cache-Control' => "public, max-age=#{1.hour.seconds.to_i}"
+    "Cache-Control" => "public, max-age=#{1.hour.seconds.to_i}"
   }
 
   # Show full error reports and disable caching.
diff --git a/activestorage/test/dummy/config/initializers/assets.rb b/activestorage/test/dummy/config/initializers/assets.rb
index 4b828e80cb..c1f948d018 100644
--- a/activestorage/test/dummy/config/initializers/assets.rb
+++ b/activestorage/test/dummy/config/initializers/assets.rb
@@ -1,12 +1,12 @@
 # Be sure to restart your server when you modify this file.
 
 # Version of your assets, change this if you want to expire all your assets.
-Rails.application.config.assets.version = '1.0'
+Rails.application.config.assets.version = "1.0"
 
 # Add additional assets to the asset load path.
 # Rails.application.config.assets.paths << Emoji.images_path
 # Add Yarn node_modules folder to the asset load path.
-Rails.application.config.assets.paths << Rails.root.join('node_modules')
+Rails.application.config.assets.paths << Rails.root.join("node_modules")
 
 # Precompile additional assets.
 # application.js, application.css, and all non-JS/CSS in the app/assets