Merge pull request #263 from jorrit/contributelink

fix: contributing course link in CONTRIBUTING.md

Author: boazpoolman

CONTRIBUTING.md

@@ -81,7 +81,7 @@ The `package.json` file contains various scripts for common tasks:
 
 ### Sending a pull request
 
-> **Working on your first pull request?** You can learn how from this _free_ series: [How to Contribute to an Open Source Project on GitHub](https://egghead.io/series/how-to-contribute-to-an-open-source-project-on-github).
+> **Working on your first pull request?** You can learn how from this _free_ course: [How to Contribute to an Open Source Project on GitHub](https://egghead.io/courses/how-to-contribute-to-an-open-source-project-on-github).
 
 When you're sending a pull request: