Rails 5 - resque undefined method `namespace' for main:Object

Question

I was unable to run my rails server in development mode. I have installed two gems are resque and resque-scheduler into rails application. I have searched for the solution online but still, I was struggling with it.

Gemfile:

 gem 'resque'
 gem 'resque-scheduler'

Config file of application:

 config.active_job.queue_adapter     = :resque

The resque.rake file:

 require 'resque/tasks'
 require 'resque/scheduler/tasks'

 namespace :resque do
    puts "Loading Rails environment for Resque"
  task :setup do
    require 'resque'
    require 'resque-scheduler'

    Resque.redis = 'localhost:6379'
  end
 end