Web IDE Markdown Preview displays broken images

Summary

When using the Preview Markdown in the Web IDE, images are displayed as broken links.

Steps to reproduce

  • Open a Web IDE project which has a markdown document.
  • Link to an image in a relative fashion. I.e, ![](./relative_image.png) or ![](relative_image.png)
  • Select the Preview Markdown tab.
  • Notice that the image is broken

Note: this is also broken on gitlab.com.

Example Project

https://gitlab.com/cetra3/web-ide-issue

What is the current bug behavior?

The image appears as a broken link

What is the expected correct behavior?

It should display the image as per the file view.

Relevant logs and/or screenshots

Screenshot_2019-05-02_IDE

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:         Ubuntu 16.04
Current User:   git
Using RVM:      no
Ruby Version:   2.5.3p105
Gem Version:    2.7.6
Bundler Version:1.17.3
Rake Version:   12.3.2
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.5
Go Version:     unknown


GitLab information
Version:        11.10.4
Revision:       62c464651d2
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     PostgreSQL
DB Version:     9.6.11
URL:            https://...
HTTP Clone URL: https://.../some-group/some-project.git
SSH Clone URL:  git@...:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: yes

Possible fixes

Not sure!