Only adds the deprecator in the app if Rails supports it

Fixes #329.

Author: rafaelfranca

lib/web_console.rb

@@ -28,6 +28,10 @@ module WebConsole
   def self.logger
     (defined?(Rails.logger) && Rails.logger) || (@logger ||= ActiveSupport::Logger.new($stderr))
   end
+
+  def self.deprecator
+    @deprecator ||= ActiveSupport::Deprecation.new("5.0", "WebConsole")
+  end
 end
 
 require "web_console/railtie"

lib/web_console/railtie.rb

@@ -52,7 +52,7 @@ class Railtie < ::Rails::Railtie
     end
 
     initializer "web_console.deprecator" do |app|
-      app.deprecators[:web_console] = ActiveSupport::Deprecation.new("5.0", "WebConsole")
+      app.deprecators[:web_console] = WebConsole.deprecator if app.respond_to?(:deprecators)
     end
 
     initializer "web_console.permissions" do
@@ -67,7 +67,7 @@ def web_console_permissions
       when config.web_console.allowed_ips
         config.web_console.allowed_ips
       when config.web_console.whitelisted_ips
-        Rails.application.deprecators[:web_console].warn(<<-MSG.squish)
+        WebConsole.deprecator.warn(<<-MSG.squish)
           The config.web_console.whitelisted_ips is deprecated and will be ignored in future release of web_console.
           Please use config.web_console.allowed_ips instead.
         MSG