Fixed wrong command on configuring ufw, change ufw add rule to ufw allow rule

Author: CristianoYL

guides/DigitalOcean Tutorial.md

@@ -20,7 +20,7 @@ DigitalOcean is a cloud infrastructure provider focused on simplifying web infra
 
 ## Creating an account
 
-You can sign up to DigitalOcean using our affiliate link. Doing so gives you a starting credit of $10, which allows you to rent a server for 2 months. Click this link to create your account and get the $10: [https://m.do.co/c/d54c088544ed](https://m.do.co/c/d54c088544ed). If the link doesn't work, paste it into your browser. 
+You can sign up to DigitalOcean using our affiliate link. Doing so gives you a starting credit of $10, which allows you to rent a server for 2 months. Click this link to create your account and get the $10: [https://m.do.co/c/d54c088544ed](https://m.do.co/c/d54c088544ed). If the link doesn't work, paste it into your browser.
 
 ![Create an account](assets/DigitalOcean/create_account.png)
 
@@ -277,8 +277,8 @@ sudo ufw status
 If not, we will enable it later. Before that, let's add some new rules:
 
 ```
-sudo ufw add 'Nginx HTTP'
-sudo ufw add ssh
+sudo ufw allow 'Nginx HTTP'
+sudo ufw allow ssh
 ```
 
 **Important:** the second line, adding SSH rules, is not related to nginx configuration, but since we're activating the firewall, we don't want to get blocked out of the server!