CURL is not installed in your php installation

 Open Terminal:  
      1. You have to need fisrt install CURL using sudo apt-get install curl  
      2. Now restart Apache by typing sudo service apache2 restart  
      3. Then install PHP5 CURL by typing sudo apt-get install php5-curl  
      4. It will ask yes or no so type y or yes!  
      5. Finally restart apache using second line command.