Merge branch 'docs-render-keyboard-shortcut' into 'master'

render help keyboard shortcut correctly

See merge request gitlab-org/gitlab-ce!28286

doc/workflow/shortcuts.md

 # GitLab keyboard shortcuts
 
-You can see GitLab's keyboard shortcuts by using 'shift + ?'
+You can see GitLab's keyboard shortcuts by using <kbd>shift</kbd> + <kbd>?</kbd>
 
 ## Global Shortcuts