Fix rubocop complaint

Gemfile

@@ -2,4 +2,4 @@ source "https://rubygems.org"
 
 gemspec
 
-gem 'rails'
+gem "rails"

Rakefile

@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 require "bundler/gem_tasks"
-require 'rake/testtask'
+require "rake/testtask"
 
 Rake::TestTask.new(:test) do |t|
   t.libs << "test"
   t.libs << "lib"
-  t.test_files = FileList['test/**/*_test.rb']
+  t.test_files = FileList["test/**/*_test.rb"]
   t.verbose = true
 end
 
-task :default => :test
+task default: :test

test/env_test.rb

@@ -1,4 +1,4 @@
-require 'webpacker_test'
+require "webpacker_test"
 
 class EnvTest < Minitest::Test
   def test_current_env

webpacker.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency "bundler", "~> 1.12"
   s.add_development_dependency "minitest", "~> 5.0"
-  s.add_development_dependency "rake", '~> 12.0'
+  s.add_development_dependency "rake", "~> 12.0"
 
   s.files         = `git ls-files`.split("\n")
   s.test_files    = `git ls-files -- test/*`.split("\n")