Update to PHP 7

sudo add-apt-repository ppa:ondrej/php
sudo apt-get install -y language-pack-en-base
sudo LC_ALL=en_US.UTF-8 add-apt-repository ppa:ondrej/php

sudo apt-get update
sudo apt-get install php7.0
sudo apt-get install php7.0-mysql

sudo apt-get install php7.0-mbstring
sudo apt-get install libapache2-mod-php7.0

sudo apt install php libapache2-mod-php

sudo a2dismod php5
sudo a2enmod php7.0

sudo apt-get install php-xml 
sudo apt-get install php7.1-mbstring
sudo apt-get install php7.0-intl

sudo apt-get install php7.0-curl php7.0-mbstring php7.0-zip php7.0-xml
sudo apt-get install php7.0-apcu-bc
sudo phpenmod apcu

https://www.digitalocean.com/community/tutorials/how-to-upgrade-to-php-7-on-ubuntu-14-04

https://askubuntu.com/questions/760907/upgrade-to-16-04-php7-not-working-in-browser