Nextcloud version: improve readability

scripts/install

 #!/bin/bash -eux
 
+NEXTCLOUD_VERSION=15.0.4-fpm
 MYSQL_ROOT_PASSWORD=`tr -dc A-Za-z0-9_ < /dev/urandom | head -c 20 | xargs`
 NEXTCLOUD_ADMIN_PASSWORD=`tr -dc A-Za-z0-9_ < /dev/urandom | head -c 20 | xargs`
 
@@ -12,5 +13,5 @@ echo "SMTP_PASSWORD=${MAIL_PASS}" >> .env
 echo "MAIL_FROM_ADDRESS=${MAIL_USER}" >> .env
 echo "SMTP_NAME=${MAIL_USER}" >> .env
 echo "NEXTCLOUD_ADMIN_PASSWORD=${NEXTCLOUD_ADMIN_PASSWORD}" >> .env
-echo "NEXTCLOUD_VERSION=15.0.4-fpm" >> .env
+echo "NEXTCLOUD_VERSION=${NEXTCLOUD_VERSION}" >> .env
 echo "MYSQL_VERSION=5.7" >> .env