Change http link to https.

Author: HonkingGoose

book/08-customizing-git/sections/config.asc

@@ -45,7 +45,7 @@ $ man git-config
 ----
 
 This command lists all the available options in quite a bit of detail.
-You can also find this reference material at http://git-scm.com/docs/git-config.html[].
+You can also find this reference material at https://git-scm.com/docs/git-config[].
 
 ===== `core.editor`