Merge branch 'wiki-bottom-padding' into 'master'

Add padding to bottom of wiki page, fix #12921.

## What does this MR do?
Adds padding to the bottom of the wiki page so it's not right up against the edge of the browser window.

## What are the relevant issue numbers?
#12921

## Screenshots (if relevant)

Before:

![Screen_Shot_2016-06-06_at_12.21.22_PM](/uploads/9710682a57f5e521253f17a65f896f4d/Screen_Shot_2016-06-06_at_12.21.22_PM.png)

After:

![Screen_Shot_2016-06-06_at_12.20.50_PM](/uploads/002068b072050e0f8146757a0386d30f/Screen_Shot_2016-06-06_at_12.20.50_PM.png)

cc: @jschatz1 

See merge request !4490

app/views/projects/wikis/show.html.haml

@@ -18,7 +18,7 @@
     You can view the #{link_to "most recent version", namespace_project_wiki_path(@project.namespace, @project, @page)} or browse the #{link_to "history", namespace_project_wiki_history_path(@project.namespace, @project, @page)}.
 
 
-.wiki-holder.prepend-top-default
+.wiki-holder.prepend-top-default.append-bottom-default
   .wiki
     = preserve do
       = render_wiki_content(@page)