crontab in rails 4 not executing correctly

Question

I was developing a project(its an Intranet project for a company to check employees is working or not) in rails 4. In that I want to take the screen shots of the users logged in every 1 minute and save to server. I created methods for taking screen shot.And could save to the database.But problem is occurring in the cron tab creation. Its not executing at all. For creating crontab I used gem 'whenever', :require => false in my gem file. After that I wheneverize .it, So I got schedule.rb file.

My schedule.rb file

set :environment, 'development'

every 1.minutes do 
    runner "MyModel.cron_screenshot"
end

I want to check in development mode thats why I set environment to 'development'

MyModel is my model file contains this code

class MyModel < ActiveRecord::Base
    has_attached_file :file_avatar, :default_url => "/files/:style/missing.jpg",
      :styles => {
         :thumb => "100x100#",
         :small  => "150x150>",
         :medium => "500x500" 
       }
    do_not_validate_attachment_file_type :file_avatar



    def self.cron_screenshot
        puts pwd()
        result = %x{scrot}
        create
    end

    def create
        f = File.open(Rails.root.join('screenshot.png'), 'rb')
        model = MyModel.new
        model.file_avatar = f
        model.save
    end
end

I am using Ubuntu 13.04 as my operating system. When I entered command crontab -l to check I got the output as

# Begin Whenever generated tasks for: store
* * * * * /bin/bash -l -c 'cd /home/project/screenshot/image && bin/rails runner -e development '\''MyModel.cron_screenshot'\'''

# End Whenever generated tasks for: store

After one minute nothing is happening. What went wrong here?