PlantUML URL does not update on comments after changing its setting

Summary

When running PlantUML on a dynamic URL (such as AWS' EC2), you need to keep you PlantUML settings updated, but that won't update comments made to issues that includes PlantUML charts.

Updating the comment (by just adding a new space/line) will force gitlab to render a new URL

Steps to reproduce

  1. Setup PlantUML
  2. Make a comment to an issue and add a ```plantuml...``` fence to it
  3. Update PlantUML URL
  4. Comment will still point to the previous server

What is the current bug behavior?

Gitlab will render the comment with the wrong/old PlantUML server address

What is the expected correct behavior?

The PlantUML server address should be the same as specified on the settings file

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:         Debian 9.1
Current User:   git
Using RVM:      no
Ruby Version:   2.5.3p105
Gem Version:    2.7.6
Bundler Version:1.16.6
Rake Version:   12.3.1
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.3
Go Version:     unknown

GitLab information
Version:        11.6.1
Revision:       598c5a7
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
Using LDAP:     no
Using Omniauth: yes
Omniauth Providers: saml


GitLab Shell
Version:        8.4.3
Repository storage paths:
default:      /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks
Git:            /opt/gitlab/embedded/bin/git
Edited by Rafael Sierra