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

bin/pull_translations.rb

@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 # Usage:
 #   bundle install

lib/queries.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Queries
   def self.default
     # WARNING: Edit the query hash carefully

plugin.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # name: discourse-data-explorer
 # about: Interface for running analysis SQL queries on the live database
 # version: 0.2

spec/controllers/queries_controller_spec.rb

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