Merge branch 'documentation-bug-public-key-should-be-private-key' into 'master'

docs public key -> private key

See merge request gitlab-org/gitlab-ce!26902

doc/user/project/pages/lets_encrypt_for_gitlab_pages.md

@@ -134,7 +134,7 @@ Now that your certificate has been issued, let's add it to your Pages site:
     sudo cat /etc/letsencrypt/live/example.com/fullchain.pem | pbcopy
     ```
 
-1. Copy and paste the public key into the second field **Key (PEM)**:
+1. Copy and paste the private key into the second field **Key (PEM)**:
 
     ```bash
     sudo cat /etc/letsencrypt/live/example.com/privkey.pem | pbcopy