Update header images

- Rename image.feature to header.image

_pages/theme-setup.md

@@ -6,10 +6,6 @@ modified: 2016-01-19
 excerpt: "Instructions on how to install and customize the Jekyll theme Minimal Mistakes."
 share: true
 comments: true
-image:
-  feature: sample-image-3.jpg
-  credit: WeGraphics
-  creditlink: http://wegraphics.net/downloads/free-ultimate-blurred-background-pack/
 ---
 
 {% include toc.html %}