Problem: When linking to the raw version of a Gist, the link changes with each revision.
Solution:
https://raw.github.com/gist/[gist_id] returns first file from the gist.
For gist with multiple files: https://raw.github.com/gist/[gist_id]/[file_name]
The url works even when you change the filename:
Or simply use https://rawgit.com