Add frozen string literal comment to files.

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 group :development do

bin/pull_translations.rb

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

plugin.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # name: discourse-oauth2-basic
 # about: Generic OAuth2 Plugin
 # version: 0.3
@@ -64,7 +66,7 @@ class OAuth2BasicAuthenticator < ::Auth::OAuth2Authenticator
   end
 
   def json_walk(result, user_json, prop)
-    path = SiteSetting.send("oauth2_json_#{prop}_path")
+    path = SiteSetting.get("oauth2_json_#{prop}_path")
     if path.present?
       segments = path.split('.')
       val = walk_path(user_json, segments)

spec/plugin_spec.rb

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