Add frozen string literal comment to files.

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 group :development do
   gem 'translations-manager', git: 'https://github.com/discourse/translations-manager.git'
 end

app/serializers/concerns/topic_answer_mixin.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module TopicAnswerMixin
   def self.included(klass)
     klass.attributes :has_accepted_answer, :can_have_answer

bin/pull_translations.rb

@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 require 'translations_manager'
 

plugin.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # name: discourse-solved
 # about: Add a solved button to answers on Discourse
 # version: 0.1

spec/integration/solved_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 RSpec.describe "Managing Posts solved status" do

spec/models/site_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 require_dependency 'site'
 

spec/requests/topics_controller_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 RSpec.describe TopicsController do

spec/serializers/topic_answer_mixin_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe TopicAnswerMixin do