fix URL

Author: fmichonneau

_config.yml

@@ -31,7 +31,7 @@ carpentries_pages: "https://carpentries.github.io"
 carpentries_site: "https://carpentries.org/"
 dc_site: "http://datacarpentry.org"
 example_repo: "https://github.com/carpentries/lesson-example"
-example_site: "https://carpentries.github.com/lesson-example"
+example_site: "https://carpentries.github.io/lesson-example"
 lc_site: "https://librarycarpentry.github.io/"
 swc_github: "https://github.com/swcarpentry"
 swc_pages: "https://swcarpentry.github.io"