Upgrade rubocop

test/integration/document_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 class DocumentTest < Minitest::Test
@@ -5,14 +7,14 @@ class DocumentTest < Minitest::Test
 
   def test_unexpected_outer_tag
     exc = assert_raises(SyntaxError) do
-      Template.parse("{% else %}")
+      Template.parse('{% else %}')
     end
     assert_equal exc.message, "Liquid syntax error: Unexpected outer 'else' tag"
   end
 
   def test_unknown_tag
     exc = assert_raises(SyntaxError) do
-      Template.parse("{% foo %}")
+      Template.parse('{% foo %}')
     end
     assert_equal exc.message, "Liquid syntax error: Unknown tag 'foo'"
   end