Update the kickstart link

Instead of pointing at a specific (in this case actually non-working!) revision, point to the github UI for the
head revision.
The user is expected to find the 'raw' link there, but the page allows to also quickly look at changes etc, which
might be helpful for people unfamiliar with kickstart files.

website/source/docs/builders/qemu.html.markdown

@@ -60,7 +60,7 @@ paths to files, URLS for ISOs and checksums.
 </pre>
 
 A working CentOS 6.x kickstart file can be found
-[at this URL](https://gist.github.com/mitchellh/7328271/raw/c91e0c4fa19c171a40b016c6c8f251f90d2ad0ba/centos6-ks.cfg), adapted from an unknown source.
+[at this URL](https://gist.github.com/mitchellh/7328271/#file-centos6-ks-cfg), adapted from an unknown source.
 Place this file in the http directory with the proper name. For the
 example above, it should go into "httpdir" with a name of "centos6-ks.cfg".