Update LinuxInstall.md for Ubuntu 18.04

Ubuntu 18.04 uses PHP 7.2.
Depreciated php-mcrypt is gone now.

docs/LinuxInstall.md

@@ -20,6 +20,12 @@ You may need to start by updating the system repositories
 
     sudo apt-get install apache2 mysql-server mysql-client php libapache2-mod-php php-mysql php-curl php-pear php-dev php-mcrypt php-json git-core redis-server build-essential php7.0-mbstring -y
 
+**For Ubuntu 18.04:**
+
+*PHP 7.2*
+
+    sudo apt-get install apache2 mysql-server mysql-client php libapache2-mod-php php-mysql php-curl php-pear php-dev php-json git-core redis-server build-essential php7.2-mbstring -y
+
 ### Install PHP pecl dependencies
 
 *Not essential, required for mail sending e.g. password recovery*
@@ -37,6 +43,11 @@ You may need to start by updating the system repositories
     printf "extension=redis.so" | sudo tee /etc/php/7.0/mods-available/redis.ini 1>&2
     sudo phpenmod redis
 
+ **If running PHP7.2:** Add pecl modules to php7.2 config
+
+    printf "extension=redis.so" | sudo tee /etc/php/7.2/mods-available/redis.ini 1>&2
+    sudo phpenmod redis
+
 ### Configure Apache
 
 Emoncms uses a front controller to route requests, modrewrite needs to be configured: