Fix link to substack blog post in README

Author: kimmobrunfeldt

README.md

@@ -20,7 +20,7 @@ Like `npm run watch-js & npm run watch-less` but better.
 
 ## Why
 
-I like [task automation with npm](http://substack.net/task_automation_with_npm_run)
+I like [task automation with npm](https://github.com/substack/blog/blob/master/npm_run.markdown)
 but the usual way to run multiple commands concurrently is
 `npm run watch-js & npm run watch-css`. That's fine but it's hard to keep
 on track of different outputs. Also if one process fails, others still keep running