SVGs are not allowed to render in documentation

Summary

Trying to load any of the SVG images in the documentation / help pages results in a 404 error

Steps to reproduce

Try to view one of the pages with SVGs in the images, /help/ci/pipelines.md for instance, note that the "Types of Pipelines" image (/help/ci/img/types-of-pipelines.svg) doesn't load - and indeed is a 404 if trying to visit it directly.

What is the current bug behavior?

The image fails to load with a 404 error

What is the expected correct behavior?

The image loads and is displayed correctly

Relevant logs and/or screenshots

This bug happens on GitLab.com

Possible fixes

https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/controllers/help_controller.rb#L41

Adding :svg to the list of formats seems to solve the issue, tested on one local CE install.