add php7.2 repo if on stretch

install.sh

@@ -40,6 +40,14 @@ fi
 
 ### Install required packages
 log_running "Installing required packages..."
+
+raspbian_version="$(lsb_release -c --short)"
+
+if [ "$raspbian_version" == "stretch" ]; then
+    wget -q https://packages.sury.org/php/apt.gpg -O- | sudo apt-key add -
+    echo "deb https://packages.sury.org/php/ stretch main" | sudo tee /etc/apt/sources.list.d/php7.list
+fi
+
 sudo apt update -yq
 sudo apt install -yq predict \
                      python-setuptools \