updating [how-contribute] url

Author: abostroem

CONTRIBUTING.md

@@ -111,7 +111,7 @@ email][contact].
 [github]: https://github.com
 [github-flow]: https://guides.github.com/introduction/flow/
 [github-join]: https://github.com/join
-[how-contribute]: https://egghead.io/series/how-to-contribute-to-an-open-source-project-on-github
+[how-contribute]: https://egghead.io/courses/how-to-contribute-to-an-open-source-project-on-github
 [issues]: https://carpentries.org/help-wanted-issues/
 [lc-issues]: https://github.com/issues?q=user%3ALibraryCarpentry
 [swc-issues]: https://github.com/issues?q=user%3Aswcarpentry