update php version in ubuntu code example

Example 1: change php version ubuntu

//In ubunutu
Default PHP 7.1 is set on your system and you need to switch to PHP 5.6

$ sudo a2dismod php7.1
$ sudo a2enmod php5.6
$ sudo service apache2 restart
  
sudo update-alternatives --set php /usr/bin/php5.6

Example 2: change php version ubuntu

$ sudo update-alternatives --config php
 or
$ sudo a2enmod php7.1(version)