update to node 15 ubuntu code example

Example 1: updating node js ubuntu

curl -sL https://deb.nodesource.com/setup_14.x | sudo -E bash -
sudo apt-get install -y nodejs

Example 2: ubuntu update nodejs

# Using Ubuntu
curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
sudo apt-get install -y nodejs

# Using Debian, as root
curl -sL https://deb.nodesource.com/setup_12.x | bash -
apt-get install -y nodejs